Concrete pavement often experiences accelerated deterioration due to water and chemical ingress through micro-cracks and surface voids. Particularly, the ingress of aggressive agents into the concrete matrix results in irreversible changes and deterioration on its endurance. Numerous studies unveiled that hydrophobic surface protection could be an inexpensive and effective way of enhancing the durability of concrete. This research work aims to assess the feasibility of bio-cement posttreatment for facilitating hydrophobic surface protection, thus enhancing the performance and durability of concrete blocks. Enzyme induced carbonate precipitation (EICP) is one of the promising bio-cement methods. Concrete blocks casted in four different grades were subjected to EICP treatment with different treatment schemes and recipes of cementation media. The treated blocks were tested for water absorption, ultrasonic pulse velocity (UPV) measurements, unconfined compressive strength (UCS), thermal performance, and scanning electron microscopy (SEM). The results indicated that the concrete blocks subjected to EICP posttreatment showed over a 55% reduction in water absorption, a 15% higher UCS and a 6.7% higher UPV when compared with control blocks. The SEM analysis suggested that the EICP posttreatment could enhance the durability of concrete paving blocks by enabling a layer of calcite on the surface and by plugging the transport pore channels of the concrete. Although most of the posttreatment strategies investigated herein were found to be operative, a better response was seen in the posttreatment by spraying scheme with 0.5 mol/L cementation media (CM). With the successful demonstration, the EICP treatment prior to the use of concrete blocks can be recommended to the pavement construction industry.

With further investigation on biomineralization, biomimetic mineralization has been proposed in imitation of microorganism behavior, in which the mechanism of biomineralization is utilized for the control of the crystal growth to synthesize inorganic materials with special structures and superior physical-chemical properties. This review summarizes the recent advances in biomimetic-chemically induced carbonate precipitation (BCICP). BCICP is a biomimetic mineralization process induced by calcium carbonate crystal modifiers, which directly regulates the metathesis reaction of calcium salts with carbonates in soils to improve the soil properties. Several crystal modifiers for BCICP, including the aspartic acid (organic), the boric acid (inorganic), and the polyacrylic acid (polymer), are reviewed, and the biomimetic mineralization mechanism is introduced. In addition, current findings about BCICP in cementitious materials, soil reinforcement, dust suppression, as well as other fields are discussed, aiming to give deeper insights into the further development and application of BCICP.

This paper presents a microdevice developed to measure the electrical conductivity of a liquid or a saturated porous medium using Wenner method. It is developed in the context of biocementation as soil improvement technique, which is used in Civil Engineering applications to produce calcium carbonate through bacterial or enzymatic activity, replacing the use of other binder materials such as cement or resins, and therefore reducing carbon footprint. The microdevice was used to measure urease activity in the soil interstitial fluid, to investigate if bacterial activity could be affected by the presence of the particles and tortuosity from pore geometry. Such analysis is important to understand biocementation mechanism inside the soil and helps to improve the design of such treatment solutions. The device is basically a squared reservoir printed in polypropylene using a 3D printing machine, incorporating stainless steel electrodes in its base. The electrical resistivity was computed adopting Wenner method, by connecting 4 PCB electrodes to a signal generator and an oscilloscope for measuring the voltage when a AC current of 1 mA was applied. Both square and sinusoidal waves with 5 kHz frequency were selected among other frequencies. The measurements were adjusted during the calibration of the microdevice, done using standard salt solutions with known electrical conductivity measured using an electrical conductivity probe. For the bacterial activity measurements, the bacterial and urea solutions were added to a uniform-graded size quarzitic sand (average diameter 0.3 mm) placed inside the microdevice and covering completely the electrodes. Bacterial activity was not affected by the presence of the sand, which confirms that this treatment is effective for this type of soils.

Repeated wet swelling and dry shrinkage of soil leads to the gradual occurrence of cracks and the formation of a complex fracture network. In order to study the development characteristics and quantitative analysis of cracks in root-soil complex in different growth periods under dry-wet cycles, the alfalfa root-loess complex was investigated during different growth periods under different dry-wet cycles, and a dry-wet cycle experiment was conducted. The crack rate, relative area, average width, total length, and the cracks fractal dimension in the root-soil complex were extracted; the crack development characteristics of plain soil were analyzed under the PG-DWC (dry-wet cycle caused by plant water management during plant growth period), as well as the crack development characteristics of root-soil complex under PG-DWC and EC-DWC (the dry-wet cycles caused by extreme natural conditions such as continuous rain); the effects of plant roots and dry-wet cycles on soil cracks were discussed. The results showed that the average crack width, crack rate, relative crack area, and total crack length of the alfalfa root-loess complex were higher than those of the plain soil during PG-DWC. The result indicated that compared with plain soil during PG-DWC, the presence of plant roots in alfalfa root-soil complex in the same growth period promoted the cracks development to some extent. The alfalfa root-soil complex crack parameters during different growth periods were relatively stable during PG-DWC (0 dry-wet cycle). During EC-DWC (1, 3, and 5 dry-wet cycles), the alfalfa root-loess complex crack parameters increased with the number of dry-wet cycles during different growth periods. Unlike PG-DWC, the EC-DWC accelerated crack development, and the degree of crack development increased with the number of dry-wet cycles. The existence of plant roots promoted crack development and expansion in the root-soil complex to a certain extent, and the dry-wet cycle certainly promoted crack development and expansion in the root-soil complex. This result contradicts the improvement in the root-soil complex's macro-mechanical properties during plant growth, due to differences in the mechanical properties of roots and soil. The research results will provide reference for the root soil complex crack development law and the design of slope protection by vegetation.

Soil improvement is one of the most important issues in geotechnical engineering practice. The wide application of traditional improvement techniques (cement/chemical materials) are limited due to damage ecological environment and intensify carbon emissions. However, the use of microbially induced calcium carbonate precipitation (MICP) to obtain bio-cement is a novel technique with the potential to induce soil stability, providing a low-carbon, environment-friendly, and sustainable integrated solution for some geotechnical engineering problems in the environment. This paper presents a comprehensive review of the latest progress in soil improvement based on the MICP strategy. It systematically summarizes and overviews the mineralization mechanism, influencing factors, improved methods, engineering characteristics, and current field application status of the MICP. Additionally, it also explores the limitations and correspondingly proposes prospective applications via the MICP approach for soil improvement. This review indicates that the utilization of different environmental calcium-based wastes in MICP and combination of materials and MICP are conducive to meeting engineering and market demand. Furthermore, we recommend and encourage global collaborative study and practice with a view to commercializing MICP technique in the future. The current review purports to provide insights for engineers and interdisciplinary researchers, and guidance for future engineering applications.

With the increasing demand for buildings and infrastructures and the mounting challenges associated with the current construction technologies such as high emission, high pollution, and high energy consumption, the civil engineering profession is at the crossroad for a transformation or upgrading before it can be put into tasks for these challenges. Inspired by the concept of harmonious coexistence between humans and nature, a new concept, biogenic construction, for civil engineering is proposed in this paper. The definition of biogenic construction is given. The framework and four components of biogenic construction are established. These include microbial construction, plant construction, animal construction, and bioinspired construction. Examples of each component are given. A new construction system for creating a more eco-friendly, healthier, and more sustainable environment for future civil engineering developments is also proposed.

MICP (Microbially induced calcite precipitation), an environmentally friendly soil improvement technique, has great potential in ocean engineering due to its ability to promote the precipitation of calcium carbonate through microbial activity to enhance the engineering properties of geomaterials. In this study, piezocone penetration test (CPTU) is used to evaluate the effectiveness of MICP treatment in calcareous sand. The change of physical properties (relative density D_r and total unit weight γ_t) of MICP treated calcareous sand is investigated by conducting CPTU on the geomaterials prepared in a series of mini calibration chambers (25 cm × 50 cm). Results indicate that CPTU (tip stress, sleeve friction, and porewater pressure) measurements can be used to interpret the physical characteristics of calcareous sand treated with MICP under seawater conditions. Additionally, a relationship between CPTU measurements, physical parameters (relative density D_r and total unit weight γ_t) of MICP treated calcareous sand is proposed and calibrated. The findings of the research extend the implementation of in-situ testing techniques such as CPTU towards physical property evaluation of bio-treated geomaterials in ocean environment, and demonstrate the potential of scaling up MICP techniques for broader engineering application.