大宗工业副产品或废弃物(如粒化高炉矿渣、粉煤灰等)作为辅助胶凝材料用于硅酸盐水泥及混凝土中已有不短的时间。利用辅助胶凝材料可有效缓解水泥生产所带来的制备能耗高、自然资源消耗大、二氧化碳排放等问题。在胶凝材料性能不大幅降...大宗工业副产品或废弃物(如粒化高炉矿渣、粉煤灰等)作为辅助胶凝材料用于硅酸盐水泥及混凝土中已有不短的时间。利用辅助胶凝材料可有效缓解水泥生产所带来的制备能耗高、自然资源消耗大、二氧化碳排放等问题。在胶凝材料性能不大幅降低的前提下,要实现大比例取代(≥30%(质量分数))硅酸盐水泥,激发辅助胶凝材料的活性是关键。然而,从材料学观点出发,过往基于宏观性能的经验测试方法,对辅助胶凝材料活性的理解仍相当碎片化。除比表面积等物理性质外,多数辅助胶凝材料的水硬活性取决于其中玻璃相的溶解-沉淀反应。辅助胶凝材料中的玻璃体结构可简化为网络调整体(如Ca、Na等)和网络形成体(如Si、Al等)的物质的量比,如解聚度。近来对Ca OSi O2-Al2O3体系玻璃体的研究,进一步增强了对玻璃体聚合度的理解。玻璃体的溶解与聚合程度及溶液组成(如溶液的饱和程度、阴阳离子类型及浓度、p H等)密切相关。同时,沉淀的生成也会显著改变玻璃体的溶解动力学。本文归纳了辅助胶凝材料玻璃体结构与水硬活性的研究进展,分别对表征辅助胶凝材料玻璃体结构的解聚度及玻璃体中Si(Qn(m Al))聚合程度进行了介绍,分析了玻璃体结构在不同激发条件下的反应活性,以期为制备性能稳定和耐久性优良的低碳建筑材料提供参考。展开更多
The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonat...The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation 展开更多
A silica fume, precipitated silica, metakaolin and siliceous fly ash behavior as constituents of mortars was studied, while mortar samples have been tested for long-term alkali-silica reaction expansion in accordance ...A silica fume, precipitated silica, metakaolin and siliceous fly ash behavior as constituents of mortars was studied, while mortar samples have been tested for long-term alkali-silica reaction expansion in accordance to the GOST 8269.0 specification. Solid-state 29Si-MAS NMR spectroscopy and thermogravimetric analysis were used to describe Portland cement hydration, supplementary cementitious material pozzolanic reaction and to establish a structure of products of those processes. It was found that long-term test conditions, in contrast to the accelerated test, do not affect the composition of products formed too much, compared to normal conditions. This allows results obtained with long-term test to be expected as more relevant in terms of predicting of supplementary cementitious materials inhibiting properties.展开更多
文摘大宗工业副产品或废弃物(如粒化高炉矿渣、粉煤灰等)作为辅助胶凝材料用于硅酸盐水泥及混凝土中已有不短的时间。利用辅助胶凝材料可有效缓解水泥生产所带来的制备能耗高、自然资源消耗大、二氧化碳排放等问题。在胶凝材料性能不大幅降低的前提下,要实现大比例取代(≥30%(质量分数))硅酸盐水泥,激发辅助胶凝材料的活性是关键。然而,从材料学观点出发,过往基于宏观性能的经验测试方法,对辅助胶凝材料活性的理解仍相当碎片化。除比表面积等物理性质外,多数辅助胶凝材料的水硬活性取决于其中玻璃相的溶解-沉淀反应。辅助胶凝材料中的玻璃体结构可简化为网络调整体(如Ca、Na等)和网络形成体(如Si、Al等)的物质的量比,如解聚度。近来对Ca OSi O2-Al2O3体系玻璃体的研究,进一步增强了对玻璃体聚合度的理解。玻璃体的溶解与聚合程度及溶液组成(如溶液的饱和程度、阴阳离子类型及浓度、p H等)密切相关。同时,沉淀的生成也会显著改变玻璃体的溶解动力学。本文归纳了辅助胶凝材料玻璃体结构与水硬活性的研究进展,分别对表征辅助胶凝材料玻璃体结构的解聚度及玻璃体中Si(Qn(m Al))聚合程度进行了介绍,分析了玻璃体结构在不同激发条件下的反应活性,以期为制备性能稳定和耐久性优良的低碳建筑材料提供参考。
文摘The issue of concrete carbonation has gained importance in recent years due to the increase use in supplementary cementing materials (SCMs) in concrete mixtures. While there is general agreement that concrete carbonation progresses at maximum at a relative humidity of about 60%, the rate may differ in the case of cements blended with SCMs, especially with high-volume fly ash replacements. In this study, the effect of high-volume fly ash concrete exposed to low ambient relative humidity (RH) conditions (57%) and accelerated carbonation (4% CO2) is investigated. Twenty-three concrete mixtures were produced varying in cementitious contents (310, 340, 370, and 400 kg/m3), water-to-cementitious materials ratio (0.45 and 0.50), and fly ash content (0%, 15%, 30%, and 50%) using a low and high-calcium fly ash. The specimens were allowed 1 and 7 days of moist curing and monitored for their carbonation rate and depth through phenolphthalein measurements up to 105 days of exposure. The accelerated carbonation test results indicated that increasing the addition of fly ash also led to increasing the depth of carbonation. Mixtures incorporating high-calcium fly ash were also observed to be more resistant against carbonation than low-calcium fly ash due to the higher calcium oxide (CaO) content. However, mixtures incorporating high-volume additions (50%) specimens were fully carbonated regardless of the type of fly ash used. It was evident that the increase in the duration of moist curing from 1 day to 7 days had a positive effect, reducing the carbonation depth for both plain and blended fly ash concrete mixes, however, this effect was minimal in high-volume fly ash mixtures. The results demonstrated that the water-to-cementitious ratio (W/CM) had a more dramatic impact on carbonation resistance than the curing age for mixtures incorporating 30% or less fly ash replacement, whereas those mixtures incorporating 50% showed minor differences regardless of curing age or W/CM. Based on the compressive strength results, carbonation
文摘A silica fume, precipitated silica, metakaolin and siliceous fly ash behavior as constituents of mortars was studied, while mortar samples have been tested for long-term alkali-silica reaction expansion in accordance to the GOST 8269.0 specification. Solid-state 29Si-MAS NMR spectroscopy and thermogravimetric analysis were used to describe Portland cement hydration, supplementary cementitious material pozzolanic reaction and to establish a structure of products of those processes. It was found that long-term test conditions, in contrast to the accelerated test, do not affect the composition of products formed too much, compared to normal conditions. This allows results obtained with long-term test to be expected as more relevant in terms of predicting of supplementary cementitious materials inhibiting properties.
