Evaluation of Freeze-Thaw Durability of Silica Fume Concrete with Spraying Inorganic Coating Using Ultrasonic Testing

To study the antifreezing durability of internal coating silicon fume concrete with different external coatings, fast freeze-thaw (FT) cycle testing was performed for three types of external coatings applied to the internal coatings of silicon fume concrete. Using ultrasonic testing and compressive strength tests, we analysed the relationships between the ultrasonic pulse velocity and the mechanical and physical properties of concrete under freeze-thaw action. The results show that the compressive strength and pulse velocity of the studied concrete changed little before the first 100 FT cycles but varied significantly after being subjected to 100 FT cycles and diminished linearly with increasing FT cycles. The dynamic elastic parameters of the concrete were inferred using pulse velocity calculations, and the dependence on FT cycles was very similar to that of ultrasonic pulse velocity. The concrete strength was strongly and positively correlated with ultrasonic pulse velocity. The linear regression model of between ultrasonic pulse velocity, kinetic coefficient, and compressive strength of concrete was also established. The damage incurred to the external coating material (XT-HPA + XT-SS and XT-HPS) was small, and the good performance of the concrete with the added inorganic coating after freeze-thaw cycles indicates good frost resistance.

Performance of Green Concrete and Inorganic Coating Materials

Green concrete (GC) was developed for realizing sustainable development, recycling waste materials, and reducing environmental pollution. For the practical use of GC, various harmful materials must blocked from entering its cracks and pores; and its strength and durability must be improved. The use of an inorganic coating material (ICM) for GC effectively prevents the intrusion of harmful materials and repairs the concrete. ICMs can reduce the permeability and increase the durability of concrete. This study investigated GC, construction waste, and ICMs and used recycled sand and gravel as well as construction waste as substitutes for cement. The results indicate that the coarse aggregate substitution, water-binder ratio, and recycled fine aggregate substitution must be controlled suitably in GC. Furthermore, the coating layer, fine aggregate substitution, and aging of the ICM mut be controlled suitably. GC with an ICM showed poorer performance than conventional concrete, mainly because of the high porosity. Nonetheless, the ICM somewhate reduces the porosity and resists the penetration of chloride ions, thereby promoting concrete quality.

One-Part Plastic Formable Inorganic Coating Obtain from Alkali-Activated Slag /Starch(CMS) Hybrid Composites

Coating technology can be applied to decorate building constructions. Alkali-activated materials (AAM) are promising green and durable inorganic binders which show potential for development as innovative coating. In the paper, the possibility of using AAM composited with starch (CMS) as a novel plastic formable inorganic coating for decorating in building was investigated. The rheological properties, including plastic viscosity, yield stress, and thixotropy were considered to be critical properties to obtain the working requirements. Four different mixtures were systematically investigated to obtain the optimum formulation, and then were used to study their hardened properties, such as mechanical strengths (compressive, flexural, and adhesive strength), drying shrinkage, cracking behavior, and microstructure. Study results found that CMS could quickly and efficiently be hydrolyzed in an alkaline solution to produce organic plastic gel which filled in AAM paste, leading to the significant improvement of coating consistency, plastic viscosity, and thixotropy. The optimum coating composited with 15.40 wt% CMS shows a relatively stable rheological development, the setting time sufficient at higher than 4 h. Furthermore, CMS shows a significant positive effect on the cracking and shrinkage control due to padding effect and water retention of CMS, which results in no visible cracks on the coating surface. Although the mechanical strength development is relatively lower than that of plain AAM, its value, adhesive strength 2.11 MPa, compressive strength 55.09 MPa, and flexural strength 8.06 MPa highly meet the requirements of a relevant standard.