Search

Attack of sulfate crystallization and chemical interaction between sulfate and hydration product is one of the most important factors responsible for degradation of cementitious materials. This study investigates the effects of emulsified asphalt and fly ash as well as their combination on resistance of mortar to physicochemical attack of sulfate in order to develop high performance cementitious materials with high resistance to sulfate attack. The partly-submerged experiment with 5% Na2SO4 solution is designed to simulate physicochemical attack of sulfate salt on sample. Results indicate that, compared with fly ash, addition of emulsified asphalt is more effective in improving the resistance of mortar sample to physical crystallization role and chemical attack of sulfate. Moreover, a combination of fly ash and emulsified asphalt can further enhance the resistance of cementitious materials to physicochemical attack of sulfate, which results from the improvement of microstructure, reduction of CH product and increase of ductility of sample.

In order to investigate transportation of sulfate solution in concrete and its influence factors, transportation velocity and crystallization areas of sulfate solution in concrete, porosity and pore structure of concrete were tested by methods of transportation crystallization test and evaporable water test. Results show that under temperature (20±2)°C and relative humidity (60±5)％ environment, sulfate solution permeate concrete wall and get to concrete surface in very short time. The decrease of water to binder ratio and addition of mineral mixture to concrete can decrease transportation velocity and crystallization areas of sulfate solution in concrete. The transportation velocity and crystallization areas have great correlation with concrete porosity with pore dia. > 30nm.

The deterioration mechanism of sulfate attack on cement- based materials under partial soaking condition is very complex. This paper investigated the surface morphology, microstructure and corrosion products in different zones of cement mortar under 5% sulfate solution partial soaking condition at 360 d by methods of SEM, EDS and XRD, respectively. Results show that under partial soaking condition, cement mortar are distinguished four zones – soaking zone, wet zone, crystallization zone and dry zone. Corrosion products in soaking zone and wet zone are predominantly ettringite, showing chemical corrosion take place in those zones. Corrosion products in crystallization zone are gypsum and crystals of Na2SO4 and Na2SO4.10H2O, showing both sulfate chemical corrosion in high concentration and physical crystallization attack occur in this zone. However, there is no any corrosion product founded in dry zone.

An extensive research programme was set up to investigate the efficiency of scrap rubber particles on strength of cementitious materials. The index of strength loss rate of paste and mortar sample caused by increasing 1% volume rubber particles was proposed to analyze the efficiency of rubber particles in cementitious materials. And the corresponding mechanism was also discussed in this paper. Results indicate that in the investigated area, the loss rate in compressive strength both for paste and mortar almost ranges from 2% to 5% caused by increasing 1% rubber particles depending on the total volume of rubber particle added into sample. However, the loss rate in flexural strength of mortar by increasing 1% volume rubber particles is obviously different from that. Three roles of scrap rubber particles played in cementitious materials, named as deformation effect, equivalent-pore effect and hydrophobic effect, are responsible for the efficiency of scrap rubber particles on strength of cementitious material. The efficiency of rubber particles on strength of paste and mortar differs from each other due to the different microstructure between paste and mortar.

Several experiments were carried out to investigate the effects of water to binder ratio(w/b) and mineral admixtures on water sorptivity and permeability of new-old concrete composite system in this paper in order to further understand the transport properties and thus degradation mechanism of new-old concrete repair system. Results indicate that a reasonable choice of w/b of new concrete is of great importance for obtaining new-old concrete composite with a low water sorptivity. Addition of ultrafine powder such as silica fume as one of component of repairing materials will benefit for effectively reducing water sorptivity and permeability of new-old concrete repair system in practice. The linear correlative coefficient between capillary sorption coefficient, coulomb electricity and porosity of new-old concrete composite sample is bad and lower compared with those of corresponding new concrete samples. The total porosity of new-old concrete composite sample is not an exclusive factor determined its water sorptivity and permeability. The pore structure of new-old concrete composite sample, especially interfacial transition zone between new and old concrete plays more important role on transport properties of sample.

In precast concrete elements manufacturing, steam-cured concrete incorporating 30% fly ash encountered the problem of a too low demoulding compressive strength. To resolve it, this paper developed a new steam-cured concrete (AFSC) incorporating fly ash and a chemical activator. Experiments were conducted to investigate the mechanical properties of AFSC. The corresponding mechanism was also discussed by testing the microstructure of concrete. Results indicate that the demoulding compressive strength of AFSC can meet production requirements, and compressive and flexure strength of AFSC at later ages increase well. Compared with that of ordinary steam-cured concrete, AFSC has a higher tensile strength, and the capability of AFSC to resist cracks is enhanced remarkably. At an early age, addition of the chemical activator can distinctly accelerate the extent of hydration of the fly ash cement systems, and thus the microstructure of concrete becomes denser.