Effect of mineral additives and permeability reducing admixtures having different action mechanisms on mechanical and durability performance of cementitious systems

Abstract

In this paper, the effect of usage of the permeability reducing admixture (PRA) having different action mechanisms on hardened state properties of cementitious systems containing mineral additives is examined. For this aim, three commercial PRAs were used during investigation. The effective parameters in the first and third PRAs were air-entraining and high-rate air-entraining, respectively. The second one contained the insoluble calcium carbonate residue and had a small amount of the air-entraining property. Mortar mixes with binary and ternary cementitious systems were prepared by partially replacing cement with fly ash and metakaolin. The hardened state properties of mortar mixtures such as compressive strength, ultrasonic pulse velocity, water absorption, drying shrinkage and freeze–thaw resistance were investigated. The ternary cement-based mixture having both fly ash and metakaolin was selected as the most successful mineral-additive bearing mix in regard to hardened state properties. In this sense, PRA-B, with both insoluble residues and a small amount of air-entraining properties, showed the best performance among the mixtures containing PRA. The combined use of mineral additive and PRA had a more positive effect on the properties of the mixes.

Graphical abstract

Keywords

cementitious system / mineral additive / permeability reducing admixture / mechanical properties / durability performance

1 Introduction

Concrete quality and performance have improved with concrete production technology progress in recent years. The use of chemical admixtures was inevitable in producing high strength concrete [ 1, 2] and researchers have carried out various studies to enhance the fresh and hardened properties of cementitious systems [ 3– 5]. On the other hand, concrete manufacturers compete with each other to produce the most compatible admixture with the cement used in the market, so as not to cause cement-admixture incompatibility.

The most important parameter in concrete production with a long service life is concrete’s low void ratio [ 6]. The void structure and void ratio of concrete are directly connected with the permeability of the concrete mixtures. Due to the high permeability of concrete, aggressive substances may enter its structure. For example, in a sulfate attack, sulfate waters penetrate the concrete cavities and cause harmful chemical reactions [ 7– 9].

It is necessary to understand the mechanism of water movement in concrete. Fluid motion in concrete occurs in three ways. These are:

i) complete filling of cavities with water results in saturated flow under the influence of water pressure [ 10, 11];

ii) where the cavities are partially filled with water, surface tension forces are generated and unsaturated current (capillarity) arises [ 12, 13];

iii) water vapor flow takes place due to the vapor pressure difference [ 12, 14].

Concrete permeability varies according to the capillary void ratio and whether these voids are independent of each other [ 15]. Parameters such as mixing ratio, interfacial transition zone (ITZ), aggregate permeability and curing conditions affect concrete permeability. Besides, shrinkage cracks that occur due to differences in ambient temperature and humidity significantly affect concrete permeability [ 16– 18]. Concrete’s resistance to sulfate [ 9], acid [ 19], carbonation [ 20], reinforcement corrosion [ 21], freeze–thaw [ 20] and alkali-silica reaction depends on its permeability to a significant extent [ 22]. Therefore, the permeability and diffusivity coefficient of concrete are the most critical factors affecting the service life of the concrete structure [ 15]. Diffusivity is expressed in terms of the transition transfer of ions from regions of higher density to regions of lower density in the concrete [ 23]. Liquid or powdered water impermeability admixtures with different mechanisms are used to reduce the permeability of concrete mixtures [ 15]. Some of the admixtures in question (permeability reducing admixtures (PRAs)) are added to the concrete in fresh form and provide impermeability by filling the capillary gaps. Further material, waterproofing admixture, can be added to the concrete or applied to the specimen surface. The action mechanism of the mentioned admixtures is to provide impermeability by giving concrete water repellency [ 24]. Today, some mineral additives are used to reduce concrete permeability and to improve its durability performance as with chemical admixtures. Since the advent of higher fineness of mineral additives, and their pozzolanic activity, the utilization of mineral additives improves concrete permeability by reducing capillary voids and improving the ITZ [ 25, 26].

Felekoğlu and Baradan [ 27] investigated the use of water impermeability admixtures consisting of modified lignosulfonate (LS) and organic fatty acid ester mixture (WRC) in concrete mixtures. The organic fatty acid ester creates a hydrophobic layer on the walls of the cavities formed within the concrete and prevents the water from moving into the interior, so the WRC is better than the LS in terms of permeability reduction of concrete. Akyol [ 28] has produced five different concrete mixes in total by using impermeability admixtures up to 0.5%, 1%, 1.5%, and 2% of cement weight to determine the parameters affecting the permeability of concrete and to investigate the effect mechanism. According to the results, the minimum water requirement and maximum compressive strength were obtained with the 2% impermeability admixture since the water/cement ratio is lower than the other mixtures. Since admixtures are air-entraining, the highest unit weight was obtained in the control mixture. Mardani-Aghabaglou et al. [ 29] examined the influence of different types of PRA on concrete compressive strength and permeability. They emphasized that the use of PRA increases the compressive strength of mixtures and decreases the permeability value. This decrease was more evident in mixtures with a lower w/c ratio. Yıldırım et al. [ 30] identfied that using PRA positively affects the permeability of mixtures, but increasing the cement dosage negatively affects the permeability of mixtures. Moralıoğlu [ 31] disovered that the viscosity of mortar mixtures increased with the use of biopolymer admixture and negatively affected the workability. Furthermore, he stated that there is no incompatibility in terms of cement additive workability with the use of water reducing admixtures in mortar mixtures containing biopolymer, and that he observed increases in the compressive strength of mixtures. In addition, he said that the strength loss caused by the use of excessive amounts of water reducing admixtures in the mixes was prevented by the use of the kit and the wear loss caused by freeze–thaw in mixtures containing chitin was less than other mixtures.

As is seen from the literature, different studies have been conducted on the use of mineral additives in cementitious systems. In these studies, generally plain and binary binder cementitious systems were used. However, in this research mineral additive-bearing mortar mixtures were produced by creating a ternary binder system. In addition, it has been found that there are a few studies using PRA in cementitious systems. The admixture action mechanisms have not been fully explained in these studies. However, since the action mechanisms of the admixtures used in this study are clearly known, the results have been examined in detail. This study consists of two stages. In the first stage, the effect of using different mineral additives and PRA on the hardened state properties of cementitious systems was investigated. For this purpose, two different series of mortar mixes were produced. In the first series, in addition to the control (C) mix, three different mineral additive-bearing mortar mixes were prepared by partially replacing fly ash (CF) and metakaolin (CM) with cement. In the second series, six different PRA containing mineral additive-free mortar mixtures were produced by the addition of three PRAs having different action mechanisms with the rates of 1 w.t.% and 2 w.t.% of the cement. The compressive strength, water absorption, freeze–thaw resistance, UPV test and drying-shrinkage behavior of the mortar mixes were determined. At the end of the first stage, one of the best mixes containing mineral additives and one of the best mixes containing PRA were selected in terms of hardened state properties. In the second stage of the study, the selected mineral additive and PRA were used together and a mortar mixture having a ternary binder system was prepared. The tests were carried out in the first step on the prepared mixture. While preparing the mortar mixes, the water/cement ratio, sand/binder ratio and flow values were kept constant as 0.485, 2.75, and 270 ± 20 mm, respectively.

2 Experimental study

In this section, information is given about the materials and methods used in the experimental study.

2.1 Materials

In this research, CEM I 42.5R type Portland cement conforming with EN 197-1 standard, fly ash (FA) conforming to ASTM C618, and metakaolin (MK) were used as binder and mineral additive, respectively. The chemical component of binders supplied from their producers is shown in Table 1. Also, the physical and mechanical properties of the binders used in the mixtures are listed in Tables 2 and 3, respectively. CEN Standard sand conforming to EN 196-1 was used as aggregate. The specific gravity and water absorption capacity of the limestone aggregate were designated according to EN 1097-6 Standard and are 2.72% and 0.7%, respectively.

In all mortar mixtures the flow value was constant at 270 ± 20 mm. To ensure the desired flow value, a polycarboxylate-ether-based high water-reducing admixture was used in different proportions. Besides, to determine the effect of PRA usage on cement paste and mortar mixes properties, three “PRA” commercial products provided from two different companies were used. As was mentioned earlier, six different PRA containing mineral additive-free mortar mixtures were produced by adding three PRA having different action mechanisms to the mixture at the rate of 1% and 2% of the cement. The mentioned admixtures are named “PRA-A”, “PRA-B”, and “PRA-C”. Some properties of the water reducing admixture and PRA supplied from their suppliers are given in Tables 4 and 5, respectively. When used in cementitious systems in appropriate proportions, these admixtures’ advantages are presented in Table 6. According to the information provided by the manufacturers.

PRA-A:

• Provides impermeability by entraining air in mixtures and blocking capillary gaps.

• It is recommended to use 0.4% to 0.7% by weight of the total binder in the mixture design. This ratio varies depending on cement, mineral additives, sand, and water components used in the mortar mixture design and also the desired fresh and hardened mortar properties. Therefore, laboratory tests should be done according to the desired properties and the mixing ratio should be determined.

• In case of a high admixture dosage, there may be an increase in setting time and air entrainment effect as it is known that compressive strength of cementitious system is negatively affected by increasing of air bubbles in the system.

PRA-B:

• Since it contains insoluble residue, it provides water impermeability by filling the capillary pores in the mixtures.

• It has a small amount of air-entraining properties. Therefore, it causes the capillary gaps of the mixtures to be clogged.

PRA-C:

• It is used to form an impermeable layer in mortars, plasters and screeds that require waterproofing.

• It decreases permeability by blocking the capillary pores due to its high air-entraining properties when used at an appropriate rate.

2.2 Methodology

2.2.1 Compressive strength

The 1-, 3-, 7-, 28-, and 90-d compressive strength of the mortar mixes was determined according to the ASTM C109 standard on 50 mm cube specimens. Three cubic specimens were produced for each series of the mixes. The prepared specimens were cured in water until the experiment day.

2.2.2 Water absorption capacity

The 28- and 90-d water absorption capacity of the mortar mixes was obtained on 50 mm cube specimens according to the ASTM C642-13 standard. The specimens were kept in water for 28- and 90-d and were taken from the water, their surfaces were dried with a towel and their saturated surface dry weight b was measured. After that, they were dried in a 105 °C oven to constant weight and dry weight a was measured. The water absorption values of the mortar mixes was determined in accordance with Eq. (1). Also, the amount of air content of the mortar mixes was investigated in accordance with TS EN 12350–7 Standard. The air meter device was used to measure the air percentage of the mortar mixtures.

(1) \text{water absorption} ( \mathrm{\%} ) = \left(\frac{b-a}{a}\right) \times 100 .

2.2.3 Ultrasonic pulse velocity (UPV)

The UPV values of the specimens were measured before the freeze–thaw cycle according to TS EN 12504-4 standard and then measured every 50 cycles. Thus, the freeze–thaw-induced variation of the UPV values in the specimens was measured up to 300 cycles and plotted. In this experiment, after applying gel on the smooth surfaces of the specimens and with the frequency adjusted to 250 kHz, measurements were made with small probes. There is no direct relationship between the speed of the P wave passing through the material and the strength of the material. However, there is a certain relationship between the velocity of the P wave and the density of the mortar. In mortar mixtures with low density and with more voids in them, the P wave takes longer to reach from one surface of the samples to the other. In other words, as the amount of voids inside the mortar increases, the velocity of the P wave becomes lower. The UPV value of the specimens after curing in water for 28 d and 90 d was determined. The dynamic modulus of elasticity of the specimens was obtained from Eq. (2) depending on the UPV values.

(2) E_{\text{dn}} = \rho c^2 \frac{(1+v)(1-2v)}{(1-v)} ,

where E _dn is dynamic modulus of elasticity of concrete (MPa), ρ is density of the hardened concrete (kg/m ³), c is ultrasonic pulse velocity (UPV) (km/s) and v is poisson ratio. The poisson ratio of concrete in all mixtures was taken as 0.22.

2.2.4 Freeze–thaw resistance

The freeze–thaw resistance of the mixtures was carried out according to ASTM C666 standard. In the study, the fast method was applied, freezing in air and thawing in water. The freezing and thawing temperatures in the test are in the range of −18°C ± 2°C and 5°C ± 2°C, respectively. The freeze–thaw test was set as 9 stages, the freezing time (the time to reach the minimum temperature from the maximum temperature) was set as 200 min, and the time from the minimum temperature to the maximum ambient temperature was set as 60 min. This process, lasting 260 min, was one freeze–thaw cycle. Before the freeze–thaw cycle, the weights of the samples were measured. The samples were weighed every 50 cycles. Thus, weight changes in samples subjected to freeze–thaw up to 300 cycles were calculated.

The freeze–thaw resistance of the mixes was compared using two different methods. In the first method, the weight loss of each mixture after every 50 freeze–thaw cycles were measured. This process was repeated up to 300 freeze–thaw cycles. In the second method, the UPV values of the mixtures up to 300 cycles were measured after every 50 freeze–thaw cycles. Thus, the durability factors of the mixtures were calculated with Eq. (3).

(3) D_{\text{f}} = \frac{n}{3} \left(\frac{E_{\text{dn}}}{E_{\text{d0}}}\right) ,

where n is number of cycles, E _dn is dynamic modulus of elasticity of the specimen after 300 freeze–thaw cycles, E _d0 is dynamic modulus of elasticity of the specimen before being exposed to freeze–thaw cycles.

2.2.5 Drying–shrinkage

25 mm × 25 mm × 285 mm prismatic specimens were produced to determine the drying-shrinkage properties of the mixtures. The produced specimens were demoulded after 24 h and cured in water at 20 °C for 28- and 90-d. Then they were taken out of the curing pool and kept in a room with a temperature of 20°C and a relative humidity of 55%. The length changes of prismatic specimens were calculated according to ASTM C596-01 standard.

2.3 Preparation of mortar mixtures

Mortar mixes were prepared according to ASTM C109 Standard. In all mixtures, water/binder ( w/ b) and sand/binder ( s/ b) ratios as well as flow values were kept constant as 0.485, 2.75, and 270 ± 20 mm, respectively. As it was stated earlier, a polycarboxylate-ether based high range water reducing admixture was used to provide the required flow value. To determine the influence of PRA and mineral additive on some properties of mortar mixes, binary and ternary cementitious systems were formed. In addition to the control mixture (C) without any additives, mixtures containing PRA and mineral additive were prepared. In the first and second series of binary binder systems, 20% and 10% CF and CM by weight were replaced with cement. In the third series, on the other hand, mortar mixtures named CFM with ternary binder systems were used by replacing fly ash and metakaolin at 20% and 10% of cement weight, respectively. Then, by adding three PRAs having different action mechanisms at the rate of 1 and 2 w.t.% of the cement to the control mixture, six different PRAs were produced. Mixtures are named according to the PRA name and usage rate (Table 7). For example, the mortar mixture containing 1% “PRA-A” is represented by “PRA-%1A”. However, the mixture containing 2% by weight of cement “PRA-A” is shown as “PRA-%2A”. All mixtures are homogeneously prepared by Hobart mixer. The preparation process of the mixtures is summarized below.

1) Water was mixed with cement at a (slow) speed of 62 r/min for 30 s.

2) The mixer was stopped and any cement paste that adhered to the sides of the mixer bowl and did not mix was stripped off with a spatula.

3) The mixture was stirred at 125 r/min (fast) for 2 min. Therefore, it was incorporated for 2.5 min in total in mixtures without additives.

4) In the mixtures containing additives, each additive was added by the three methods described above and mixed for 2 min at 125 r/min (fast).

3 Results

As mentioned earlier, the study was conducted in two stages. The results obtained in the first and second stages of the study are given under two subtitles.

3.1 First stage results

In the first stage of the study, the effect of usage of mineral additive and PRA on the hardened state properties of mortar mixtures was determined. For this purpose, two different series of mortar mixes were produced. In the first series; the mortar mixtures having plain, binary and ternary binder systems were prepared by partially substituting fly ash and metakaolin instead of cement. In the second one, mortar mixtures containing 1% and 2% of three commercial PRA having different action mechanisms were produced.

3.1.1 Compressive strength

The 1-, 3-, 7-, 28-, and 90-d compressive strength results of the mortar mixes bearing mineral additives and PRA are shown in Figs. 1 and 2, respectively. Each final result was the average of three measurements. Irrespective of the mineral additives and PRA types and utilization rates, compressive strength of the mortar mixtures increased day by day.

Compared to the control mixture, substitution of 20% fly ash and 10% metakaolin instead of cement had no significant effect on the 1-d compressive strength of the mixtures. However, the 1-d compressive strength of the “CFM” mixture having ternary binder system in which fly ash and metakaolin were used together was about 40% lower than that of control mixes. The reduction in 1-d compressive strength of the “CFM” mixture is due to the substitution of mineral additives for 30% of the total binder in the mixture and the pozzolanic reaction not being effective at very early ages.

1-d compressive strength of “CM” mixture having a binary binder system showed higher strength than the control mixture. As is known, the pozzolanic reaction is highly dependent on the fineness of the mineral additive and its reactive silica content. At early ages, the pozzolanic reaction is controlled by the fineness parameter. Actually, it is controlled by the reactive silica content of mineral additive in advanced ages [ 12]. The fineness of metakaolin is 40% higher than that of other binders. Therefore, in the mentioned mixture, the pozzolanic reaction started at an early age. As can be understood from Fig. 1, the difference between the compressive strength of control and “CM” mixtures became more obvious with elapsing time. The “CM” mixture showed 1%, 14%, 23%, 57%, and 51% higher performance than the control mixture in terms of 1-, 3-, 7-, 28-, and 90-d compressive strength, respectively. Supporting these results, researchers have proven that replacing cement partially with metakaolin in concrete significantly increases early age strength [ 32– 34].

Up to 28 d, the “CF” mixture containing 20% fly ash displayed a lower compressive strength than the control mixture, however, at the end of 90 d, it indicated approximately 10% higher compressive strength. According to Table 2, the fineness of fly ash is closer to cement. Therefore, its pozzolanic reaction effect was more effective at late ages. The “CFM” mixture having a ternary binder system showed lower strength than the control mixture for up to 7 d. However, beyond this age, it behaved more successfully than the control mixture in terms of compressive strength. This positive effect became more pronounced with elapsing time. Bai et al. [ 35] also demonstrated that the loss of workability due to the presence of metakaolin in the CFM mixture can be improved by the inclusion of fly ash. Therefore, the CFM mixture outperformed CM and CF mixtures in terms of compressive strength. In other words, the rapid reaction of metakaolin compensates for the lower early strength of fly ash [ 36].

As already mentioned, three PRAs having different action mechanisms were used in this study. The manufacturer reported that the action mechanisms of “PRA-A” and “PRA-C” as creating permanent air bubbles in the mixture at an appropriate inter-bubble spacing of-bubbles. Distance between bubbles are independent from each other. The “PRA-B” contained insoluble calcium carbonate residue and had a small amount of air entrainment agent. It was expected that the air-entraining behavior of the admixture would reduce compressive strength of the cementitious systems owing to an increase in the amount of voids in the mixtures. A similar effect was observed in mixtures containing “PRA-A” and “PRA-C” having only air-entraining properties. As can be seen from Fig. 2, irrespective of mortar age, the mixture containing the “PRA-A” and “PRA-C” showed 12% and 10% lower compressive strength than the control mixture, respectively. This effect became more pronounced by increasing admixture utilization rate from 1% to 2%, due to the increase in the void ratio. Compared to the control mixture, the 90-d compressive strength of the “PRA-%2A” and “PRA-%2C” mixture was 20% lower. Since PRA-A and PRA-C are air-entraining, it is considered that when these admixtures is increased, the void ratio in the mixture increases.

Compared to the control mixture, the compressive strength of the “PRA-B” mixtures were not affected by the presence of 1% admixture. However, a slight increase was observed in the compressive strength values in the case of 2% of the “PRA-B”. This admixture had two different effects on compressive strength. The first was that it adversely affected the strength performance as it caused an increase in the void ratio of the mixture due to its air-entraining properties. The second one is that since it contained insoluble residue, it physically filled the micro-voids in the mixture, therefore, it positively affected the compressive strength. The fact that compressive strength values were not affected negatively with the use of the “PRA-B” indicates that the second effect was more dominant. According to the test results, it was more appropriate to use this admixture at a rate of 2% in terms of strength properties. As is shown in Figs. 1 and 2, the most successful mortar mixtures were “PRA-B” and “CM”.

3.1.2 Water absorbtion capacity

Water absorption capacity of the mortar mixtures is listed in Fig. 4. Each value represents the average of three sample measurements. The 28-d water absorption capacity values of mineral additive-bearing mortar mixtures were lower than that of the control mixture, except for the “CF”. This value for “CF” mixture was measured 4% higher than the control mixture.

Irrespective of mineral additive type, the water absorption capacity of mineral additive-bearing mortar mixture was lower than that of control mixture at the end of the 90-d test. The positive effect of mineral additive on transport properties of mortar mixture became more pronounced with elapsing time. As can be understood from the results, the “CFM” mixture showed the best performance in terms of water absorption capacity. This behaviour was due to the physico-chemical effect of the mineral additive. The mentioned mixture contained 30% mineral additive. Since its grains/particles are physically finer than those of cement, they caused a decrease in permeability by blocking the gaps. Saboo et al. [ 37] indicated that replacing more than 20% of cement with fly ash and metakaolin can reduce the porosity of concrete. Chemically, due to the pozzolanic reaction of the mineral additive, the CHs were transformed into C-S-H and a dense mortar mixture was formed [ 36]. Thus, the permeability of the mixture was decreased. Although the mentioned mechanism was effective from an early age, it became more dominant with time. In this context, the use of metakaolin was more effective than fly ash. The 28- and 90-d pozzolanic activity index of fly ash was measured as 78% and 91%, respectively. This value was obtained as 105% and 110% for metakaolin, respectively.

It was observed that the use of PRA generally decreased the water absorption capacity of the mortar mixtures. By adding 1% of the “PRA-A” to the mixture, 10% and 24% reductions were identified in the 28- and 90-d water absorption capacity compared to the control mixture, respectively. These reduction values were obtained as 4% and 15% for 28- and 90-d ages mortar upon the presence of 2% PRA-A in the system. Permeability reducing performance of PRA-A was negatively affected by increasing admixture content from 1% to 2%. This negative effect is considered to be caused by the formation of non-uniform voids in the mixture as a result of excessive air-entrainment. It can be understood from Fig. 3 that the air content of the mixture increased from 2.9% to 5.5% with the increased admixture usage rate from 1% to 2%.

Compared to the control mixture, 7% and 17% reductions in 28- and 90-d water absorption capacity were obtained by addition of 1% of the “PRA-B” to the mixture. This reduction rate was obtained as 13% and 30% upon the presence of 2% “PRA-B” in the system. As can be seen from the results, the permeability properties of the mixtures were positively affected by the increase in the usage rate of the admixture from 1% to 2%. This positive effect is considered to be a result of the increase in the amount of insoluble residue contained in the admixture due to the increase in the usage rate, the voids are physically blocked by these residues. With the increased usage rate of the admixture from 1% to 2%, the mixture air content decreases from 3.10% to 1.55% (Fig. 3).

Compared to the control mixture, the 28- and 90-d water absorption capacity of mixtures decreased by 7% by addition of 1% “PRA-C” to the mixture. In the case of adding 2% “PRA-C”, although the 28-d water absorption capacity of mixtures increased 8%, the 3% reduction was determined for 90-d ages mortar. The water absorption capacity of the mortar mixtures was negatively affected for increasing the “PRA-C” utilization rate from 1% to 2%. As emphasized earlier, this negative effect is considered to be caused by the formation of voids which are not distributed uniformly, as a result of excessive air-entrainment in the mixture upon increasing admixture content. It is also understood from Fig. 3 that with the increased usage rate of the “PRA-C” from 1% to 2%, the air content of the mixture increased from 4.9% to 7.4%.

3.1.3 Ultrasonic pulse velocity (UPV)

The 28- and 90-d UPV test results are presented in Tables 8 and 9, respectively. However, only 90-d UPV measurements were conducted for PRA-bearing mixtures. Concrete quality was determined by referring to the assessment proposed by Erdoğan [ 38] on the UPV values of concrete mixtures-concrete quality.

As shown in Table 8, irrespective of the mineral additive type and amount, the 28-d UPV values of all mineral additive mixtures were higher than that of the control mixture. The 28-d UPV of mineral additive mortar mixtures ranges from 4.46–4.54 km/s. This range became wider with time. The UPV value of the control mixture was measured as 4.20 km/s and found in good concrete quality according to the evaluation determined by Erdoğan [ 38]. No significant change was observed between the 28- and 90-d UPV of the control mixture.

Compared to the control mixture, the 28- and 90-d UPV values of the “CF” mixture containing 20% fly ash were obtained 6% and 11% higher, respectively. These rising values were measured as 8%, 12% and 7%, 15% for the “CM” and “CFM” mixture, respectively. According to Table 9, the “CM” mixture was chosen as the most successful mixture in terms of 28- and 90-d UPV performance. As highlighted earlier, metakaolin has the highest Blaine specific surface and pozzolanic activity index compared to other binders. Therefore, the porosity of the mixture improved.

UPV values of the “PRA-B” are better than those of the control mixture. Since the “PRA-B” contains insoluble residue, it physically blocks the mixture’s micro-gaps and positively affects the UPV values. However, since “PRA-A” and “PRA-C” were air-entraining, they increased the void ratio and negatively affected the UPV of the mortar specimens. The mentioned effect was more pronounced by increasing PRA utilization level.

3.1.4 Freeze–thaw resistance

The freeze–thaw resistance of mortar mixtures was investigated by monitoring weight loss, UPV and dynamic modulus of elasticity variation. For this aim, measurement of the mentioned properties was conducted every 50 cycles. Besides, the durability factor of mortar mixtures was obtained at the end of exposure to 300 freeze–thaw cycles. Each value was calculated as the average of three measurements. The weight loss during exposure to freeze–thaw cycles of mortar mixtures containing different amounts of mineral additive and PRA are shown in Figs. 5 and 7, respectively. The relative weight loss of the mentioned mixtures is given in Figs. 6 and 8, respectively.

Not surprisingly, irrespective of mineral and chemical admixtures utilization and age of mixtures, the weight loss values of mixtures increased by increasing freeze–thaw cycles. The 28-d mineral additive-bearing mortar mixtures showed the lowest performance in terms of weight loss. The relative weight loss for “CF”, “CM”, and “CFM” mixtures were 24%, 39%, and 33%, respectively. According to Table 2, the fineness of the mineral additive is higher than that of cement. It is expected that the freeze–thaw behavior of the cementitious system positively affects the increase in the amount of fine materials due to the improved pore system. However, the adverse effect of mineral additives-bearing mortar mixtures is due to not exactly incomplete pozzolanic reactions during 28 d.

As can be seen from Fig. 8, regardless of the mineral additive type and utilization rate, 90-d ages mineral additive-bearing mortar mixtures showed better performance than the control mixture in terms of weight loss. At the end of 300 freeze–thaw cycles, the 90-d relative weight losses for “CF”, “CM”, and “CFM” mixtures were measured as 13%, 8%, and 28%, respectively. This behavior is in part due to the higher fineness of mineral additive compared to that of cement and in part due to the formation of extra C-S-H resulted from the pozzolanic reaction during the 90-d period [ 36]. The “CFM” mixture having a ternary binder system containing both fly ash and metakaolin was chosen as the best mixture in terms of weight loss due to frost action. As mentioned earlier, the mentioned mixture had the lowest permeability value compared to other ones.

Irrespective of specimen age, all PRA-bearing mortar mixtures showed higher performance than the control mixture in terms of freeze–thaw dependent weight loss. This positive effect became more evident with elapsing time. As emphasized before, all PRA used in this study had air-entrainment characteristics. Therefore, the freeze–thaw resistance of mortar mixtures increased. The weight loss of 90-d “PRA-A” and “PRA-C” mixtures was 40% lower than that of the control mixture. Also, these mixtures showed about 20% lower freeze–thaw resistance than the “PRA-B” mixture. “PRA-B” mixture having 62% less weight loss compared to the control mixture was chosen as the mixture with the best performance in terms of freeze–thaw resistance at the end of 300 freeze–thaw cycles (Fig. 8). With the increase in the use of PRA from 1% to 2%, the freeze–thaw-induced weight loss performance of the mixtures was strongly affected.

The 28- and 90-d UPV values of the mixtures having mineral additives exposed to freeze–thaw cycles are given in Table 10, respectively. Based on the test results, specimens containing mineral additives showed higher UPV values than the control specimen, regardless of the mortar’s age. This behavior was more obvious over time. At the end of 300 freeze–thaw cycles, the UPV values of the “CF”, “CM”, and “CFM” mixtures were 14%, 21%, and 17% higher than the control mixture, respectively. For 90-d age mortars, these ratios were 20%, 26%, and 23% higher, respectively. The better performance of 90-d specimens compared to 28-d ones is due to an increase in the degree of pozzolanic reaction with elapsed time. It is understood from Table 10 that the “CM” mixture showed the highest UPV performance during 300 freeze–thaw cycles.

The UPV values of PRA mixtures exposed to 300 freeze–thaw cycles are given in Table 11. As can be seen from the table, the “PRA-B” mixture showed the highest UPV performance during freeze–thaw cycles. However, the UPV values of the other PRA mixtures were close to those of the control mixture up to 100 cycles. Beyond the mentioned cycle numbers, they showed slightly higher performance. This behavior became more pronounced by increasing PRA utilization level. According to the results, the mineral additive mortar mixtures showed better performance compared to PRA containing mixtures, in terms of UPV behavior.

The 90-d dynamic modulus of elasticity results of mortar mixtures are reported in Fig. 9. The dynamic modulus of elasticity of the “CF”, “CM”, and “CFM” mixtures were measured as 20%, 29%, 22%, and 44%, 56%, 52% higher than the values for the control mixture at the end of 300 freeze–thaw cycles, respectively. The characteristics of aggregate, cement paste and ITZ are the important factors affecting the dynamic modulus of elasticity of the cementitious system [ 15]. As is known, the use of mineral additives improves the ITZ due to their physico-chemical effect created in the mixtures. Therefore, the porosity volume of the mixture decreases. As is known that, the mentioned chemical effect of mineral additive is more effective at late ages, depending on its fineness. It is also understood from the results that the “CM” mixture containing 10% metakaolin shows superior performance in terms of dynamic modulus of elasticity from the early ages compared to mixtures containing fly ash.

As can be seen from Fig. 9, irrespective of admixture type and utilization rate mixtures containing “PRA” showed the best performance compared to the control mixture in terms of dynamic modulus of elasticity. Dynamic modulus of elasticity values of the mixtures decreased by increasing the usage rates of “PRA-A” and “PRA-C”, from 1% to 2%. However, the opposite effect was observed in the case of the “PRA-B” mixture. In this context, the “PRA-B” mixture was chosen as the best mortar mixture.

3.1.5 Drying–shrinkage

The length changes of 90-d ages mortar mixtures exposed to drying-shrinkage are shown in Fig. 10. As expected, irrespective of the type and amount of mineral additives and PRA, the initial shrinkage of mixtures was high, while over time their length changes decreased.

It is understood from Fig. 10 that the length changes of all mineral additive-bearing mortar mixtures was less than that of the control mixture from the beginning. The drying-shrinkage values of the “CF”, “CM”, and “CFM” mixtures were measured at 36%, 38%, and 50% less than that of the control mixture, respectively, at the end of the 64-d period. The fact that the shrinkage behavior of 90-d mineral additive mixtures is more successful than the control mixture is due to the physico-chemical effect of the mineral additives described earlier. As can be seen from the results, the 90-d “CFM” mixture having a ternary binder system was chosen as the most successful mixture in terms of shrinkage behavior. As mentioned earlier, the CFM mixture showed the best performance in terms of permeablity.

As can be seen from the results, a decrease was observed in the shrinkage value of the PRA containing mixture upon increasing the utilization rate of admixture from 1% to 2%. The mentioned reduction values were obtained as 18%, 33%, and 2% for “PRA-A”, “PRA-B”, and “PRA-C” mixtures, respectively. It is understood from Fig. 10 that, irrespective of the PRA type and amount, all samples containing “PRA” showed superior performance compared to the control mixture in terms of drying-shrinkage behavior. The relative drying-shrinkage values of the samples containing 1% “PRA-A”, “PRA-B”, and “PRA-C” compared to the control mixture were measured as 71%, 80%, and 88%, respectively. The drying-shrinkage value of the mentioned mixture decreased by 20%, 33%, and 7%, respectively, upon the presence of 2% PRA in the system. As can be understood from the results, irrespective of mixture ages, the mixture containing 2% “PRA-B” showed the best performance in terms of drying-shrinkage. As pointed out above, this admixture has both insoluble residue and a small amount of air-entraining charactersitics.

3.2 Second stage results

Asindicated above, this study consisted of two stages. At the end of the first stage, one of the best mixes containing mineral additives and one of the best mixes containing PRA were selected in terms of mechanical properties, durability performance and dimensional stability. Therefore, “CFM” and “PRA-%2B” mixtures were chosen. In the second stage, the “CFM-PRA-%2B” mixture having a ternary binding system (20%fly ash and 10% metakaolin) and containing 2% PRA-B admixture was prepared. The different properties of the “CFM-PRA-2%B” mixture were compared according to the results obtained during the first stage.

The 1-, 3-, 7-, 28-, and 90-d compressive strength results of the” CFM-PRA-%2B” mixture were measured as 6.95, 26.12, 46.10, 55.75, and 65.57, respectively. Although the 1-d compressive strength of the “CFM-PRA-2%B” mixture was about 40% less than the control mixture, its 7-, 28-, and 90-d compressive strength was 22%, 28%, and 35% higher. Compared to the CFM mixture having a ternary binder system, the 1-, 3-, 7-, 28-, and 90-d relative compressive strengths of the “CFM-PRA-%2B” mixture were measured as 99%, 117%, 117%, 109%, and 106%, respectively. Compared to the “PRA-%2B” mixture, the relative compressive strength was measured as 66%, 86%, 126%, 125%, and 128%, respectively. As a result, the combination of mineral and PRA demonstrated superior performance in terms of compressive strength compared to others. This effect is due to the positive effect of both admixtures on the void structure of the mixture.

Compared to the mixture of “C”, “CFM”, and “PRA-%2B”, the 28-d water absorption capacity of the “CFM-PRA-%2B” mixture was reduced by 25%, 8%, and 14%, respectively. This reduction ratio was measured as 40%, 9% and 16% for 90-d mixtures, respectively. As can be understood from the results, the mixture containing mineral additive and PRA together showed the highest performance in terms of water absorption capacity compared to other mixtures.

In common with the results obtained for the compressive strength and water absorption tests, the “CFM-PRA-%2B” mixture showed the best behavior in terms of UPV performance compared to other mixtures. The 90-d UPV values of the “CFM-PRA-%2B” mixture was 13%, 2%, and 8% higher than the “C”, “CFM”, and “PRA-%2B” mixtures, respectively.

Compared to the “CFM-PRA-%2B” mixture the 28-d relative weight losses of “C”, “CFM”, and “PRA-%2B” mixtures were determined as 30%, 51%, and 9%, respectively. The mentioned ratio was determined as 69%, 62%, and 10% for 90-d samples, respectively. Compared to the “C”, “CFM”, and “PRA-%2B” mixtures, the 90-d UPV values of the “CFM-PRA-%2B” mixture was 33%, 8%, and 12% higher, respectively. For the dynamic modulus of elasticity, the mentioned ratios were determined as 79%, 19%, and 28%, respectively.

The length changes of the “CFM-PRA-%2B” mixture was obtained 31%, 26%, and 16% less than that of “C”, “CFM”, and “PRA-%2B” mixtures, respectively, at the end of the 64-d period. This ratio was determined as 54%, 9%, and 54% for 90-d specimens, respectively. As can be understood from the results, the “CFM-PRA-%2B” mixture containing mineral additive and PRA together showed the best performance in terms of drying-shrinkage behavior compared to other mixtures. As mentioned earlier, the use of both mineral and PRA causes a decrease in permeability by reducing the void ratio of the mixture.

3.3 Analysis of variance

A two-way Analysis of Variance (ANOVA) was carried out to study the primary effects of two factors: age and mix type on dependent variables such as compressive strength and water absorption. The F value is obtained by dividing the variance of the group with the largest variance by the variance of the group with the smallest variance.

Tables 12 and 13 demonstrate the ANOVA outcomes of compressive strength of mortar mixtures bearing mineral additive and PRA, respectively. In mixes containing mineral additives, the P values (sig.) are approximately 0 for the mixture type and age. Thus, there is a statistically remarkable difference between these values. However, in accordance with the two-way ANOVA compressive strength results in Table 13, we statistically investigated that the mixture type and age affect the compressive strength. In addition, the mixture type and age were statistically significant because their P values were 0.069 and 0.418, respectively, larger than 0.05. The difference in the mixture type did not statistically influence the compressive strength of the mixes containing mineral additives because of the small number and similar properties of the minerals.

Tables 14 and 15 demonstrate ANOVA results of water absorption capacity of mixtures containing mineral additive and PRA, respectively. Contrary to the compressive strength, the reverse statics were obtained in the ANOVA results of water absorption of mortar mixtures bearing mineral additive and PRA. According to the ANOVA outcomes of water absorption of mortar mixtures containing mineral additive in Table 14, we statistically determined that the mixture type and age influence the water absorption. In addition, the mixture type and age were statistically significant because their P values were 0.066 and 0.12, respectively, larger than 0.05. In mixes containing PRA, the P values are approximately 0 for the mixture type and age (Table 15). Thus, there is a statistically remarkable difference between these values.

4 Conclusions

The following results were obtained in the experimental study.

1) Except for metakaolin-bearing mortar mixtures, mineral additive-containing mixtures were measured with higher compressive strength than the control mixturte up to 28-d. Beyond this day, the compressive strengths of all mineral additive including mixes were measured higher than the control one. However, except for the mixture containing PRA which contains both insoluble residues and has a weak air-entraining behaviour, the compressive strength of the mix containing other PRA was less than that of the control.

2) The 90-d water absorption capacity values of all mineral additive-bearing mortar mixtures were less than the control mixture. The mixture containing both fly ash and metakaolin showed the best performance in terms of water absorption value. The water absorption value of mixtures decreased upon the presence of 1% PRA in the system. However, an adverse effect was observed by increasing admixture content. It is consindered that this negative effect is caused by the formation of non-uniform voids as a result of excessive air entrainment in the mix. The mixtures containing the “PRA-C” admixture have 1.5 times more air content than the “PRA-A” mixtures and showed lower performance in permeability reduction.

3) Irrespective of mortar ages, the UPV behaviour of mortar mixtures improved by adding mineral additive to the control mixture. However, the presence of PRA in the system had no significant effect on the mentioned behaviour.

4) The freeze–thaw resistance of mortar mixes was increased by utilizing mineral additive and by adding PRA to the mixture. This influence was more remarkable in the presence of PRA compared to mineral additive utilization. The mixture containing fly ash and metakaolin and having a ternary binder system was chosen as the best mixture in terms of frost action between the mineral additive-bearing mixtures. In the PRA containing mixture, this effect was observed for the mix containing PRA admixture which contains both insoluble residues and has a weak air-entraining behaviour.

5) The length change of mortar mixtures was decreased by utilizing mineral additives and by adding PRA to the mixture. This influence was more remarkable in the presence of mineral additive compared to PRA utilization. The mixture containing fly ash and metakaolin and having a ternary binder system was chosen as the best mixture from the point of drying shrinkage behaviour.

6) By adding 2% PRA which contains both insoluble residues and has a weak air-entraining behavior to the mixture, including both fly ash and metakaolin, was chosen as the best mixture in terms of all properties of mortar mixes were developed.

References

[1] Cheung J, Roberts L, Liu J. Admixtures and sustainability. Cement and Concrete Research, 2018, 114 : 79– 89

[2] ACI 212.3R-10. Report on Chemical Admixtures for Concrete. Michigan: American Concrete Institute, 2016

[3] Zhan P, He Z. Application of shrinkage reducing admixture in concrete: A review. Construction & Building Materials, 2019, 201 : 676– 690

[4] Jeknavorian A J. Synergistic interaction of condensed polyacrylic acid-aminated polyether superplasticizer with calcium salts. Special Publication, 2000, 195 : 585– 600

[5] Lei L, Plank J. A concept for a polycarboxylate superplasticizer possessing enhanced clay tolerance. Cement and Concrete Research, 2012, 42( 10): 1299– 1306

[6] Uyan M, Pekmezci B V, Yıldırım H. Effects of plasticizer admixture and curing conditions on the permeability properties of concrete. Sika Technical Bulletin, 2003: 10–14 (in Turkish)

[7] Akman M S. Concrete durability and importance In: The 1st National Concrete Congress. Istanbul: TMMOB chamber of civil engineering, 1989 (in Turkish)

[8] Young J F. Review of the pore structure of cement paste and concrete and its influence on permeability. Special Publication, 1988, 108 : 1– 18

[9] Sharma R, Khan R A. Sulfate resistance of self compacting concrete incorporating copper slag as fine aggregates with mineral admixtures. Construction & Building Materials, 2021, 287 : 122985–

[10] Kocataşkın F. Vapour permeability of concrete. Bulletin of the Technical University of Istanbul, 1957, 10( 1): 53– 59

[11] Kocataşkın F. Permeability of concrete. Bulletin of the Technical University of Istanbul, 1995, 8 : 50– 56

[12] Neville A. Concrete Technology. 2nd ed. London: Longman, 1984

[13] Uyan M. Moisture movements in concrete as a hollow media. In: City Management, Human and Environmental Problems Symposium. İstanbul: TMMOB Chamber of Civil Engineering, 1988, 266–273

[14] Ehsani A, Nili M, Shaabani K. Effect of nanosilica on the compressive strength development and water absorption properties of cement paste and concrete containing Fly Ash. KSCE Journal of Civil Engineering, 2017, 21(5): 1854−1864

[15] Mehta P K, Monteiro P J M. Concrete: Microstructure, Properties and Materials. 3rd ed. New York: McGraw-Hill, 2006

[16] Choinska M, Khelidj A, Chatzigeorgiou G, Pijaudier-Cabot G. Effects and interactions of temperature and stress-level related damage on permeability of concrete. Cement and Concrete Research, 2007, 35( 1): 79– 88

[17] Gardner D R, Lark R J, Barr B. Effect of conditioning temperature on the strength and permeability of normal- and high-strength concrete. Cement and Concrete Research, 2005, 37( 7): 1400– 1406

[18] Shi C. Effect of mixing proportions of concrete on its electrical conductivity and the rapid chloride permeability test (ASTM C1202 or ASSHTO T277) results. Cement and Concrete Research, 2004, 34( 3): 537– 545

[19] Sahoo S, Mahapatra T R, Priyadarshini N, Mahapatra S, Naik S, Jaypuria S. Influence of water binder ratio on strength and acid resistance of concrete made up of mineral admixture as supplementary cementitious material. Materials Today: Proceedings, 2020, 26 : 796– 803

[20] Duc Van N, Kuroiwa E, Kim J, Choi H, Hama Y. Influence of restrained condition on mechanical properties, frost resistance, and carbonation resistance of expansive concrete. Materials (Basel), 2020, 13( 9): 2136–

[21] Shi W, Najimi M, Shafei B. Reinforcement corrosion and transport of water and chloride ions in shrinkage-compensating cement concretes. Cement and Concrete Research, 2020, 135 : 106121–

[22] Mardani-Aghabaglou A, Kalı pcı lar İ, Sezer G İ, Sezer A, Altun S. Freeze–thaw resistance and chloride-ion penetration of cement-stabilized clay exposed to sulfate attack. Applied Clay Science, 2015, 115 : 179– 188

[23] Li Z. Advanced Concrete Technology. New Jersey: John Wiley & Sons, Inc., 2011

[24] Roger Rixom R, Mailvaganam N. Chemical Admixtures for Concrete. 3rd ed. London: E & FN Spon, 1999

[25] Gruber K A, Ramlochan T, Boddy A, Hooton R D, Thomas M D A. Increasing concrete durability with high-reactivity metakaolin. Cement and Concrete Composites, 2001, 23( 6): 479– 484

[26] Valipour M, Pargar F, Shekarchi M, Khani S. Comparing a natural pozzolan, zeolite, to metakaolin and silica fume in terms of their effect on the durability characteristics of concrete: A laboratory study. Construction & Building Materials, 2013, 41 : 879– 888

[27] Felekoğlu B, Baradan B. Use of alternative waterproofing admixtures in concrete production. In: 2nd Chemical Additives in Buildings Congress Symposium Proceedings. Ankara: Chamber of Civil Engineering, 2007, 53–64

[28] Akyol K. Study on the effects of waterproofing and water repellent admixtures dosage on the water permeability of concrete and the on comperessive strengths. Thesis for the Master’s Degree. Sakarya: Sakarya University, 2008 (in Turkish)

[29] Mardani-Aghabaglou A, Tuyan M, Yı lmaz G, Arı ö z Ö, Ramyar K. Effect of different types of superplasticizer on fresh, rheological and strength properties of self-consolidating concrete. Construction & Building Materials, 2013, 47 : 1020– 1025

[30] Yıldırım H, Gülseren H, Uyan M, Kemerli K. The effect of impermeability admixtures on concrete permeability properties. In: National Concrete Congress. Istanbul: Chamber of civil engineering, 2003, 123–131

[31] Moralıoğlu M. Investigation of the effect of chemical additive-biopolymer compatibility on cement mortar properties in the specific kit. Thesis for the Master’s Degree. Manisa: Celal Bayar University, 2015 (in Turkish)

[32] Curcio F, DeAngelis B A, Pagliolico S. Metakaolin as a pozzolanic microfiller for high-performance mortars. Cement and Concrete Research, 1998, 28( 6): 803– 809

[33] Kostuch J A, Walters G V, Jones T R. High performance concrete incorporating metakaolin—A review. Concrete (London), 2000, 2 : 1799– 1811

[34] Wild S, Khatib J, Jones A. Relative strength, pozzolanic activity and cement hydration in superplasticised metakaolin concrete. Cement and Concrete Research, 1996, 26( 10): 1537– 1544

[35] Bai J, Wild S, Sabir B B, Kinuthia J. Workability of concrete incorporating pulverised fuel ash and metakaolin. Magazine of Concrete Research, 1999, 51( 3): 207– 216

[36] Pacheco-Torgal F, Shahsavandi A, Jalali S. Using metakaolin to improve the compressive strength and the durability of fly ash based concrete. In: Communications in International Conferences. Rabat: Repositórium, 2011

[37] Saboo N, Shivhare S, Kori K K, Chandrappa A K. Effect of fly ash and metakaolin on pervious concrete properties. Construction & Building Materials, 2019, 223 : 322– 328

[38] Erdoğan T Y. Concrete Materials with Questions and Answers. 1st ed. Istanbul: THBB Ready Mixed Concrete Magazine, 2003, 975−981 (in Turkish)

RIGHTS & PERMISSIONS

Higher Education Press 2021.