摘要
研究了不同掺量磷建筑石膏对硫铝酸盐水泥熟料凝结时间、化学收缩、自收缩、浆体内部相对湿度和干燥收缩的影响.结果表明:随着磷建筑石膏掺量的增加,熟料浆体的凝结时间显著缩短,化学收缩变化速率加快,浆体内部相对湿度逐渐降低,浆体自收缩与内部相对湿度具有较好的相关性;当磷建筑石膏掺量不超过25%时,硫铝酸盐水泥浆体化学收缩到达稳定阶段的时间缩短;当磷建筑石膏掺量为25%~30%时,硫铝酸盐水泥浆体在自收缩测试条件下产生膨胀,且干燥收缩小于空白组.
硫铝酸盐(CSA)水泥是在水泥熟料中掺加适量石膏和石灰石,三者共同磨细制备而成的水硬性胶凝材
磷石膏是以磷矿石为原料,湿法生产磷酸时产生的工业废弃
收缩是混凝土的一个主要特性,由收缩引起的混凝土开裂导致其使用寿命大大降
CSA水泥熟料由唐山北极熊建材有限公司生产;磷建筑石膏(PCG)来自湖北宜化集团,pH值为5.6.原材料的化学组成(质量分数,文中涉及的组成、水灰比等均为质量分数或质量比)如
采用X射线衍射仪(XRD)对未水化的CSA水泥熟料和PCG矿物组成进行分析,结果见

图1 原材料的XRD图谱
Fig.1 XRD patterns of raw materials
将质量分数为0%、5%、10%、15%、20%、25%和30%的PCG分别等质量替代水泥熟料制备试件,编号依次记作Control、PCG5、PCG10、PCG15、PCG20、PCG25和PCG30.需要说明的是,除化学收缩试验采用去离子水外,其余试验用水均为武汉市自来水.
水泥浆体的凝结时间按照GB/T 1346—2011《水泥标准稠度用水量、凝结时间、安定性检验方法》测定.由于标准稠度水泥浆体的水灰比较小,不便成型,本研究考虑到CSA水泥完全水化时的理论需水量较大,掺入减水剂会对水泥水化和体积稳定性产生影响,所选用的水灰比为0.6,此时水泥浆体的匀质性不如标准稠度水泥浆体,因此在进行终凝时间测定时不翻转试模.
水泥浆体的化学收缩根据ASTM C1608—17《Standard test method for chemical shrinkage of hydraulic cement paste》中的膨胀测定法进行测试.加水后3 h内,每隔15 min记录1次化学收缩数据;3~12 h内,每隔30 min记录1次数据;12~24 h内,每隔1 h记录1次数据;24~72 h内,每隔2 h记录1次数据,夜间除外.
采用TH10S‑B型湿度传感器(相对湿度适用范围为0%~100%)测定水泥浆体内部相对湿度变化情况.
水泥浆体的自收缩与干燥收缩采用北京仪创时代科技有限公司产YC‑JS全自动混凝土收缩膨胀仪进行测试.干燥收缩根据JGJ/T 70—2009《建筑砂浆基本性能试验方法标准》测定,将终凝后的水泥浆体试件置于(20±1) ℃、相对湿度(60±5)%的条件下进行测试,测试时间为168 h.
PCG掺量对CSA水泥浆体凝结时间的影响如

图2 PCG掺量对CSA水泥浆体凝结时间的影响
Fig.2 Influence of PCG content on setting time of CSA cement paste
当PCG掺量由5%逐渐增至30%时,PCG溶出更多的C
PCG掺量对CSA水泥浆体化学收缩及其变化速率的影响如

图3 PCG 掺量对CSA水泥浆体化学收缩及其变化速率的影响
Fig.3 Influence of PCG content on chemical shrinkage and change rate of CSA cement paste
由
由
PCG掺量对CSA水泥浆体内部相对湿度的影响如

图4 PCG掺量对CSA水泥浆体内部相对湿度的影响
Fig.4 Influence of PCG content on internal relative humidity of CSA cement paste
PCG掺量对CSA水泥浆体的自收缩及其变化速率的影响如

图5 PCG 掺量对CSA水泥浆体自收缩曲线及其变化速率的影响
Fig.5 Influence of PCG content on autogenous shrinkage and change rate of CSA cement paste
由
由
张君

图6 CSA水泥浆体自收缩与浆体内部相对湿度的关系
Fig.6 Relationship between autogenous shrinkage and internal relative humidity of CSA cement paste
根据材料各向同性原理,线性变形是体积变形的1/3,将水泥浆体单位体积的化学收缩除以3即得到线性化学收

图7 PCG15试件线性化学收缩与自收缩之间的关系
Fig.7 Relationship between linear chemical shrinkage and autogenous shrinkage of specimen PCG15
针对PCG15试件13 h后的线性化学收缩与自收缩关系进行定量分析.根据
(1) |
式中:εas(t)为CSA水泥浆体t时刻的自收缩,μm/m;εcs(t)为CSA水泥浆体t时刻的化学收缩,μm/m;εcs(t13 h)为CSA水泥浆体在13 h时的化学收缩,μm/m.
PCG试件24、48、72 h线性化学收缩与自收缩的比例关系如

图8 PCG试件24、48、72 h自收缩与线性化学收缩的比例关系
Fig.8 Ratio of linear chemical shrinkage to autogenous shrinkage of PCG specimens at 24, 48, 72 h
PCG掺量对CSA水泥浆体的干燥收缩及其变化速率的影响如

图9 PCG掺量对CSA水泥浆体的干燥收缩及其变化速率的影响
Fig.9 Influence of PCG content on drying shrinkage and its change rate of CSA cement paste
由
由
(1)PCG的掺入使得CSA水泥浆体的凝结时间显著缩短.当PCG掺量不超过25%时,CSA水泥浆体的化学收缩到达稳定阶段的时间缩短.在72 h时,随着PCG掺量的增加,CSA水泥浆体的化学收缩逐渐减小.
(2)3~28 d时,随着PCG掺量的增加,CSA水泥浆体的内部相对湿度逐渐降低.浆体内部相对湿度与其自收缩具有较好的相关性,可由浆体内部相对湿度的变化来预测自收缩变化规律. CSA水泥浆体的自收缩占化学收缩的比例随着时间的延长而降低.
(3)当PCG掺量为25%~30%时,CSA水泥浆体在自收缩测试后期表现为膨胀,且CSA水泥浆体的干燥收缩小于空白组.
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