摘要
以CO2气氛作为养护条件,研究了不同掺量的花岗岩石粉(GP)对硫氧镁(MOS)水泥性能的影响,结合X射线衍射仪(XRD)、同步综合热分析仪(TG-DSC)、扫描电镜(SEM)和压汞仪(MIP)对MOS水泥水化产物及微观结构做了分析。结果表明,碳化28 d后的掺加40% GP的MOS水泥强度保留系数提高至1.12;碳化28 d后浸水120 d强度保留系数为0.94,较空白样提高了123.8%;MOS水泥碳化过程中基体内Mg(OH)2转化为MgCO3·zH2O晶体,有利于改善MOS水泥的力学性能;GP改善了MOS水泥孔结构,提高了密实度,降低了CO2吸收率,减弱了CO2的侵蚀作用;GP和碳酸镁相的共同作用提升了MOS水泥碳化后的力学性能和耐水性。
硫氧镁(MOS)水泥是一种具有诸多优良特性的绿色建筑材
花岗岩石粉(GP)作为矿物掺合料的一种,是工业活动中产生的固体废弃物,具有产量大、易扬尘、填埋会占用大量土地资源的特
试验所用轻烧氧化镁(LBM)和七水硫酸镁(MgSO4·7H2O)均来自辽宁省;七水硫酸镁纯度>99.0%;花岗岩石粉(GP)来自湖北省;化学添加剂为柠檬酸(CA,AR);试验用水为自来水。LBM和GP的化学组成如
物质 | 化学组成 | |||||||
---|---|---|---|---|---|---|---|---|
w(MgO) | w(SiO2) | w(CaO) | w(Al2O3) | w(Fe2O3) | w(K2O) | w(Na2O) | w(其他) | |
LBM | 82.47 | 7.35 | 1.79 | 0.54 | 0.43 | 7.42 | ||
GP | 0.92 | 70.80 | 2.41 | 13.95 | 2.43 | 4.70 | 3.52 | 1.27 |
试验所用LBM活性氧化镁(a-MgO)含量使用水合法测得为65.5%;a-MgO、MgSO4、H2O摩尔比为8:1:20;CA、GP掺量以LBM质量计;CA掺量为0.5%;GP掺量从0%以10%递增至50%,试样编号则为GP0、GP20至GP50。称取LBM和GP,混合均匀后,倒入按照摩尔比配制,并静置24 h的MgSO4溶液,待搅拌均匀,倒入40 mm×40 mm×40 mm的模具内,室温下养护24 h后拆模,然后放入标准养护箱内(20 ℃±2 ℃,60%±5% RH),养护至龄期后进行测试。
试样养护至28 d后,放入40 ℃烘箱内烘烤48 h,然后在室温下,放入CO2分压为0.3 MPa的反应釜中进行碳化;将CO2通入位于反应釜中敞口容器的蒸馏水内,以使在碳化期间,反应釜内相对湿度接近100
(1) |
式中:为试样碳化或者碳化后浸水n d的抗压强度;为试样在标准养护条件下养护28 d的抗压强度。
按照
, | (2) |
式中:为试样在500~700 ℃温度区间内损失的质
使用YES-2000型万能试验机对试样抗压强度进行测试,每组试样的抗压强度取3个试样抗压强度的平均值;使用X’Pert powder型X射线衍射仪(XRD),检测MOS水泥的物相组成;利用STA 449F3型综合热分析仪(TG-DSC)探究碳化及浸水对MOS水泥水化产物含量的影响;采用ΣIGMA HD型扫描电镜(SEM)和AutoPoreIV9500型压汞仪(MIP)检测MOS水泥的微观形貌及孔隙结构。

图1 掺加GP的MOS水泥在不同养护条件的强度保留系数
Fig. 1 The strength retention coefficient of MOS cement containing GP with different curing conditions
(x)Mg(OH)2·MgSO4·(y)H2O+CO2→MgCO3+(x-1)Mg(OH)2·MgSO4·(y-1)H2O 。 | (3) |

图2 掺加GP的MOS水泥在不同养护条件的XRD图谱
Fig. 2 XRD patterns of MOS cement containing GP with different curing conditions

图3 掺加GP的MOS水泥在不同养护条件的TG-DTG曲线
Fig. 3 TG-DTG curves of MOS cement containing GP with different curing conditions
MOS水泥水化产物在升温过程中的失重变化如

图4 掺加GP的MOS水泥在不同养护条件的SEM图
Fig. 4 SEM images of MOS cement containing GP with different curing conditions

图5 掺加GP的MOS水泥在不同养护条件下的孔径分布
Fig. 5 Pore distribution of MOS cement containing GP with different curing conditions
MOS水泥在碳化过程中基体内生成较多的碳化产物和Mg(OH)2,引起膨胀,导致强度下降。掺加GP后,基体致密度提高,阻止了CO2进入基体内部,减少了基体内Mg(OH)2与CO2接触,生成的MgCO3·zH2O晶体可以填充孔隙(见
MOS水泥碳化时,其体系内存在如下所示热力学平
, | (4) |
, | (5) |
Mg(OH)2(s)⇌M | (6) |
。 | (7) |
这为MgCO3·zH2O晶体的形成提供了条件。如
掺加GP的MOS水泥碳化后力学性能提升,未掺加GP的MOS水泥碳化后力学性能及强度保留系数下降,掺加GP引起了MOS水泥碳化后性能的变化(见
1)掺加40%GP的MOS水泥碳化28 d后强度保留系数提高至1.12。未掺加GP的MOS水泥碳化28 d后浸水120 d,强度保留系数为0.42,掺加40%GP的MOS水泥强度保留系数较其提高123.8%。掺加40%GP的MOS水泥碳化后力学性能和耐水性达到最好。
2)GP减少了MOS水泥基体内部裂缝的产生,提高了基体密度,降低了MOS水泥的CO2吸收率。
3)掺加GP的MOS水泥碳化后,基体内生成的MgCO3·zH2O可以通过填充孔隙,胶联水泥颗粒,有利于改善MOS水泥碳化后的力学性能。GP和一定量的碳酸镁相共同作用提高了MOS水泥碳化后的力学性能和耐水性。Mg(OH)2转化为MgCO3·zH2O减少了MOS水泥基体内MgO水化引起的基体膨胀。
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