摘要
以花岗岩石粉(GP)为掺合料,研究了其对硫氧镁(MOS)水泥耐压强度和耐水性的影响.利用X射线衍射仪(XRD)、同步综合热分析仪、扫描电镜(SEM)、压汞仪(MIP)等研究了MOS水泥的组成、微观形貌及孔结构.结果表明:当GP掺量为30%时,MOS水泥的28 d抗压强度达到最大值,为74.1 MPa;当GP掺量为40%时,MOS水泥浸水6 d时的耐水软化系数达到最大值,为1.18;浸水溶液中M
硫氧镁(MOS)水泥由轻烧氧化镁、硫酸镁和水凝结硬化而
本文重点研究了GP对MOS水泥抗压强度和耐水性的影响,并使用万能试验机、X射线衍射仪(XRD)、扫描电镜(SEM)和压汞仪(MIP)等分析了GP的掺入对MOS水泥抗压强度、物相组成、微观结构和耐水软化系数的影响.
轻烧氧化镁粉(LBM)来源于辽宁省海城市,其活性氧化镁(a‑MgO)含量(水合法)约为65.5%(质量分数,文中涉及的含量、纯度等除特别指明外均为质量分数);花岗岩石粉(GP)来自湖北省;七水硫酸镁(MgSO4·7H2O)来自辽宁省营口市,纯度约为99.5%;外加剂为柠檬酸(CA),分析纯;试验用水为自来水,符合JGJ 63—2006《混凝土用水标准》.本试验采用外掺法确定改性剂和掺合料的掺量,即CA和GP掺量均以LBM的质量计.LBM和GP的化学组成及粒度分布见

图1 LBM和GP的粒度分布
Fig.1 Particle size distribution of LBM and GP
本试验用原材料摩尔比n(a‑MgO)∶n(MgSO4·7H2O)∶n(H2O)=8∶1∶20.将CA掺量固定为0.5%,GP掺量分别为0%、10%、20%、30%、40%和50%来制备MOS水泥试样,编号依次为C0、C10、C20、C30、C40和C50.具体制备步骤如下:按照原材料摩尔比分别称取MgSO4·7H2O和H2O,混合搅拌至MgSO4·7H2O全部溶解,得到MgSO4溶液;将称量好的CA与静置1 d的MgSO4溶液混合搅拌,得到澄清的混合溶液;将称量好的LBM与不同掺量的GP干混,待混合均匀后倒入澄清的混合溶液中,搅拌直至得到均匀的MOS混合料浆;将MOS混合料浆注入40 mm×40 mm×40 mm的模具中,置于机械振动台上振动20 s,先在室温环境下养护24 h后拆模,再放至恒温恒湿养护箱((20±2) ℃、相对湿度为(60±5)%)中养护至规定龄期.使用最大量程为300 kN的万能试验机(DYE‑300D型),对MOS水泥试件进行抗压强度测试.每组MOS水泥试件的抗压强度值取3个平行试件的平均值.
为快速评定MOS的耐水性,将养护28 d的MOS水泥试件放入50
(1) |
式中:为试件浸水n d时的抗压强度,MPa;为试件在养护箱中养护28 d的抗压强度,MPa.
首先将养护至规定龄期的试件切成3~5 mm的平整薄片,浸入无水乙醇中48 h后取出;然后放入烘箱中以45 ℃烘烤至恒重,对试样进行喷金后,即用于SEM观测.称取1.6 g试样进行MIP(AutoPoreIV9500型)测试.使用研钵将烘烤后的试样研磨成粉末进行XRD分析(5°~70°、0.02 (°)/step、X´Pert powder型)和热重分析(TG‑DTG)(45~1 200 ℃、10 ℃/min、氮气气氛、STA 449F3型)测试;使用电感耦合等离子光谱发生仪(ICP,PQ9000型)和离子色谱仪(ICS‑600型)分别测试MOS水泥试件浸水后溶液中M

图2 掺入GP后MOS水泥的抗压强度和耐水软化系数
Fig.2 Compressive strength and water resistance softening coefficient of MOS cement with GP
由
由
使用Topas6.0软件计算得到浸水前后MOS水泥中5·1·7相和Mg(OH)2的晶体尺寸,结果见

图3 不同GP掺量的MOS水泥标准养护28 d和浸水6 d时的XRD图谱
Fig.3 XRD patterns of MOS cement with different GP contents under standard curing for 28 d and soaking in water for 6 d

图4 不同GP掺量的MOS水泥标准养护28 d和浸水6 d时的TG‑DTG曲线
Fig.4 TG‑DTG curves of MOS cement with different GP contents under standard curing for 28 d and soaking in water for 6 d

图5 在不同养护条件下MOS水泥试件C0和C40的SEM照片
Fig.5 SEM images of MOS cement specimen C0 and C40 under different curing conditions
Mg(OH)2晶体表面极性和比表面积均较大,使得Mg(OH)2晶体之间容易团聚,C40的孔隙率只有2.52%,极大地压缩了Mg(OH)2晶体的生长空间.MOS水泥是碱性材料,在低温水热和碱性条件下,Mg(OH)2存在如式(
Mg(OH)2(s)Mg(OH)2(aq)Mg(OH | (2) |
Mg(OH | (3) |
H2O | (4) |
(1)GP通过微集料效应填充MOS水泥的内部气孔,优化水泥的孔结构,降低水泥基体的孔隙率,从而提高其抗压强度.当GP掺量为30%时,MOS水泥28 d抗压强度最高,可达74.1 MPa.
(2)浸出液中的M
(3)在低温水热条件下,掺入GP的MOS水泥耐水性提高的原因是:GP通过抑制MOS体系中MgO水化为Mg(OH)2,提高了MOS水泥基体的致密性;掺加GP的MOS水泥中剩余的活性MgO会继续水化生成结晶度更好的Mg(OH)2晶体;GP可填充MOS水泥的气孔,降低气孔的体积分数,抑制水分子通过气孔通道侵蚀MOS水泥基体内部.MOS水泥中掺入40%GP后浸水6 d时的耐水软化系数最大,可达1.18.
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