The Inhibiting Effect Of Admixtutes On TSA Of Concrete

The thaumasite form of sulfate attack(TSA) means that the cement concrete under the action of sulfate and carbonate were damaged by thaumasite formation. This type of damage can decompose the C-S-H gel, then the harden cement paste become a sludge mixture from the outside to the inside with strength completely lost. The harm of TSA is more serious than conventional sulfate attack.The study of experts from home and abroad on TSA had just begun, there is, disagreement about the harmfulness, corrosion mechanism and preventive measures of TSA due to complex influence factors. So It is very important for the durability of concrete by strengthening the research of prevention measures of TSA.The effects of chemical admixture and mineral admixture on TSA of cement based materials were studied in this paper. Erosion products were analyzed by way of X-ray Diffraction(XRD) and Fourier Transform Infrared Spectroscopy(FTIR).The following conclusions are reached:①The calcium formatecas can delay the TSA of harden cement paste, the resistance to TSA of mortar was increased with the content of calcium formatecas increasing in the range of 0.3% to 0.7%.②The reason why barium nitrate can inhibit the formation of thaumasite is that it capable of combining with SO42- which is the absolutely necessary reactant of forming thaumasite,so that the extent of TSA was reduced.The effect of barium nitrate on TSA of harden cement paste is closely related to its content, when incorporated 1% barium nitrate, the harden cement paste show good resistence to TSA.③The resistance to TSA of mortar was decreased with the content of sodium-polyphosphat increasing in the range of 0.3% to 1.0%. When adding calcium formatecas and barium nitrate to cement paste simultaneously, the resistance to sulfate attack can obvionsly be improved. The harden cement paste added with 0.5% calcium formatecas and 1% barium nitrate simultaneously has a good resistance to TSA. The harden cement paste added with calcium formatecas and sodium-polyphosphat simultaneously could delay the process of formation thaumasite but stop.The 0.5% calcium formatecas and 0.5% sodium-polyphosphat were used as a combination gave good results.④The effect of fly ash on TSA of harden cement paste is closely related to its chemical composition and content. The harden cement paste containing 30% of fly ash have a good resistance to TSA. ⑤To a certain extent, slag can improve the performance of resistance to TSA. The resistance to TSA of harden cement paste show best when the content of slag reach to 70%.The thaumasite form of sulfate attack of harden cement paste cut down with increased of the content of slag while the content is less than 70%.⑥Due to the high activity and filling effect, the resistance to thaumasite form of sulfate attack of mortar is remarkably improved by the addition of silica fume. It is better to resist to TSA of harden cement paste with 8% silice fume. The mineral admixture can baffle the formation of thaumasite. The improving effectiveness of mixed added of mineral admixture is better than single mineral admixture.