Cracks in concrete structures increase the penetration of water and deleterious ions, leading to accelerated deterioration. An innovative repair method using bacteria is currently gaining attention. In this method, CO2 is released by bacteria and reacts with calcium ions (Ca2+) to form CaCO3, which heals cracks by deposition. In this study, alkali-silica reaction (ASR)-induced cracks were repaired using two types of bacterial material, containing yeast and Bacillus, respectively. Microbial grouts containing these bacteria were prepared and used to impregnate mortar surfaces with ASR-induced cracks. The cracks were observed to be healed over time, and water absorption and gas permeability were reduced after repair. Thermogravimetric analysis (TGA) revealed that the main precipitate was CaCO3, while mercury intrusion porosimetry (MIP) indicated that the CaCO3 also densified the surface layer of the mortar by refining the pore structure. After repair, the specimens were immersed in water and NaOH solutions to test whether re-expansion occurred. The results showed that when immersed in 0.1 mol/L NaOH or water, the repaired specimens exhibited less expansion than the unrepaired ones.

The strength and permeability properties of various graded sand specimens grouted with superfine cement suspensions containing an additive of fine fly ash were experimentally investigated. To start with, such rheological properties as viscosity, bleeding, and setting time of superfine cement and fine fly ash mixture suspensions with various water-cement ratios (w/c) were determined. Then, the injectability tests with the mixtures were conducted on various graded sand samples. Finally, the unconfined compressive strength and the falling head permeability tests were run on the grouted specimens at different time intervals. The setting times and viscosities of superfine cement and fine fly ash mixture suspensions increased, but their bleedings were reduced. The addition of fine fly ash to superfine cement suspensions reduced the groutability of suspensions and hence increased the grouting pressure of sand specimens. The unconfined compressive strength of superfine cement grouted sand samples were increased and their permeabilities were reduced with the addition of fine fly ash. Moreover, the addition of fine fly ash to superfine cement grouts accelerated the grouted specimens’ strength gain.

Palm oil fuel ash (POFA) is a by-product procured from the palm oil mill through the incineration of empty fruit bunches, mesocarp fibers, and shells so as to produce electricity. POFA was considerably used as a cementitous supplement in various types of concrete, bricks, blocks, mortar, and grout due to its pozzolanic content. However, using raw POFA as cementitious replacement caused a distinct deterioration on the properties of the hardened mixture. Therefore, various treatment methodologies were adopted to enhance the properties of POFA to improve the mechanical properties of the hardened mixture. This study reviews the treatment approaches performed on POFA and their effects on the physical, chemical, and microstructural properties of POFA. It was documented that grinding POFA increased its fineness and decreased the voids and porosity of the mixture. However, the optimum use of grounded POFA was ranged 5 to 25% by weight of cement. On the other hand, thermal treatment of POFA exhibited a substantial improvement on the physical, chemical, and morphological properties of POFA; consequently, the hardened properties were dramatically developed. Thermal-treated POFA could be used as binder supplement up to 70% by weight of cement, whereby environmental pollution was dropped and sustainability was achieved. It was concluded that the higher fineness of POFA contributed to a significant pozzolanic reaction and thus promoted better performance in the hardened matrix. However, future detections should address the leaching behavior of POFA and the leaching performance of the hardened mixture incorporating POFA. Besides, the durability of specimens containing POFA as binder supplement should be well covered in the prospectus research.

Roller-compacted concrete (RCC) is often used to construct hydraulic structures, and in gravity dam applications, a facing system is required to control seepage along lift lines. One facing system that is gaining popularity is grout-enriched RCC (GERCC). This innovative process requires the addition of a neat cement grout to the uncompacted RCC along the face, followed by internal vibration to combine the material. One limitation of GERCC is previous research has shown difficulty in entraining air in this system. This study optimized the grout formulation to develop a stable air void system, and then evaluated the effect of this grout on the freezing-and-thawing resistance of GERCC produced both in the lab and during a field trial. Additionally, various grout placement techniques, grout dosages, and vibration levels were evaluated. The results show that freezing-and-thawing-resistant GERCC can be created when the grout and RCC are thoroughly combined.

The porous structure of manufactured structural lightweight aggregate (LWA) is responsible for differences in mechanical, durability, and thermal performance of lightweight concrete (LWC) compared to normalweight concrete (NWC). The thermal properties of LWC have not been widely studied, and publications containing values of heat capacity and thermal conductivity for LWC provide few if any details on materials, mixture proportions, and moisture states. In this study, testing was performed to determine the thermal conductivity and heat capacity of sand lightweight concrete (SLWC), alllightweight concrete (ALWC), and NWC mixtures for building and transportation applications, as well as lightweight and normalweight grout mixtures. Results of this study were evaluated then compared to published values to demonstrate the influence of this LWA on properties of the concrete and grout mixtures. Statistical models were developed to demonstrate the influence of expanded slate LWA on the thermal conductivity and heat capacity of the concrete studied.