The effect of isometric substitute of calcium hydroxide on early stage performance of alkali-activated slag concrete(AASC) was investigated.The hydration process of alkali-activated slag cement was analysed using hydration kinetics analysis,X-ray diffraction and scanning electron microcopy.The results show that the addition of Ca(OH)2 can accelerate the hydration of AASC,leading to a faster slump loss.The acceleration reaction rate constant(K) of alkali-activated slag cement increased from 4.76 × 10-5 to 5.60× 10-3 and 1.56 × 10-2 by addition of 5％ and 10％(by mass) Ca(OH)2,which shows that the addition of Ca(OH)2 mainly affects the acceleration period and the hydration induction period is shortened.Simultaneously,the reaction degree(N) decreases from 2.89 to 1.26 and 0.98,which means that the hydration process is controlled by sedimentation of reactant rather than the diffusion controlled process.The hydration process in 24 h of alkali-activated slag cement is accelerated by adding Ca(OH),with the formation of C2 ASH2 and C4 AH13.

This study investigated the immobilization potential of alkali-activated slag (AAS) pastes for Cr(VI) by examining compressive strength, toxicity characteristic leaching procedure (TCLP) and generalized acid neutralization capacity tests. Alkaline digestion, total acid digestion, XRD, FTIR and SEM-EDS were carried out to clarify the immobilization mechanism. The AAS pastes gave high compressive strengths, which contributed to the physical encapsulation of Cr. The addition of Cr(VI) induced an increase in compressive strength compared to Cr(VI)-free pastes. The leaching results showed that AAS pastes exhibited effective immobilization for Cr(VI) and that the leachability was strongly dependent on the NaOH dosage, water to slag ratio, initial Cr(VI) content, leachate pH and curing duration. The initial Cr(VI) content up to 1.5wt% by weight of slag was well immobilized with the total-Cr leachability below the TCLP regulatory limit of 5mg/L. The digestion results demonstrated that the reduction of chromium from hexavalent to trivalent played a significant role in the immobilization of Cr(VI) in AAS without any additional reductants. The XRD and SEM-EDS results suggested the formation of a clear CrO4-U phase as the primary retention phase for unreduced Cr(VI). Therefore, alkali-activated slag binder is effective in the immobilization of Cr(VI)-bearing wastes.

使用简易电阻测试法测试并计算碱矿渣混凝土不同深度的电阻率比,然后使用千分表法测试不同水胶比碱矿渣混凝土的收缩性能,并使用质量法测试同条件下碱矿渣混凝土的质量损失.建立了碱矿渣混凝土质量损失与干燥收缩之间的线性关系,探寻了碱矿渣混凝土电阻率比与质量损失之间的关系.结果表明:碱矿渣混凝土质量损失与干燥收缩之间的相关系数R2大于0.890 9,且拟合曲线的斜率与碱矿渣混凝土水胶比相关性较大;碱矿渣混凝土的电阻率比对其质量损失十分敏感,且呈正相关,因此可通过监测碱矿渣混凝土的电阻率比来评价其干燥收缩性能.

This paper presents the strength development of alkali-activated slag concrete with different water to binder ratio by the addition of Ca(OH)2 equally replacement of slag.Hydration heat test,porosity and sorptivi-ty,XRD analyses were carried out to explain the reasons of the effect of Ca(OH)2 on the strength development of AASC.By the addition of Ca(OH)2 ,the hydration process was accelerated that is the main reason of rapid early strength development,while the decrease of porosity and sorptivty indicated the pore structure was modi-fied.In addition,more calcium-rich hydration products were detected by the analysed of XRD pattern and C4 AH13 was found at the same time.