Alkali Activated Cementitious Materials, Corrosion Resistance, And Curing Of Pb <sup> 2 + </ Sup>

Alkali-activated cementing material is a new kind of cementitious materials, which can be made of blastfurnace slag,fly ash,metakaolin,steel slag,phosphorous slag or red mud. It has the merits such as saving energy, protecting environment, excellent mechanical properties and durability , it also has the ability of solidifying heavy metal, so it attract the interest of many researchers.In the investigation, the modified sodium silicate was used for alkali-activator, the metakaolin,blastfurnace slag,fly ash were used as raw materials separately. The goal of the experiment is to study the capability of solidifying heavy metal cations , the sulfate resistance capability and acid resistance property of those alkali-activated cementing materials.The result of the experiment shows the alkali-activated cements have excellent capability of solidifying heavy metal (Pb²⁺). The compressive strengths of hardened alkali-activated cementitious materials pastes with the same consistency are almost above 30MPa exclude alkali-fly ash even when Pb²⁺ content rise to 3.60%, which meet the demand of base building material or landfill. The leaching toxicity of total Pb²⁺ isn't rise with time and is less than national standard. Alkali-activated cementing remarkably decreased Pb²⁺ leaching concentration of the solidification bodies in the light of cement, the decreasing law were identical with law of capacity of NH₄⁺ ion exchange of the solidification bodies but were not related to the compressive strengths of solidification bodies materials.Accelerated test method (i.e.cycles of wetting and drying) was use to study the sulfate resistance capability of alkali-activated cementing materials. The result showed it was influenced by the curing regime of the alkali-activated cementitious materials. When the mortar specimens sealed with plastic film cured at 20℃, the relative flexural strength and relative compressive strength were high than that of Portland cement mortar specimens. But when the mortar specimens open to air and cured at 35℃, the result is contrary to the former. X-ray diffraction (XRD) analysis of the products shows that alkali-activated cementing material mortars are broken because of volume expansion produced external sodium sulfate salt-crystallization in the pore of the mortars, while ordinary Portland cement mortar is broken because of forming gypsum and external sodium sulfate salt-crystallization with volume expansion in sodium sulfate solution of 5% concentration.An experimental research on the acid resistance of alkali-activated cementing materials and Portland cement is carried out. The test results show that alkali-activated slag and fly-ash cementing materials have good acid resistance, while ordinary Portland cement and alkali-activated metakaolin have low acid resistance. It is a conclusion that the acid resistance of cementing materials is not decided by the types of the products, the acid resistance of cementing materials is not identical with law of capacity of NH₄⁺ ion exchange of the products.