摘要
普通硅酸盐水泥(OPC)是一种广泛使用的胶凝材料,但其生产会伴随大量的碳排放.为了减少碳排放,一种有效的方法就是利用固体废弃物制备新型低碳超硫水泥(SPCS)来代替OPC.废弃阴极射线管(CRT)玻璃作为固废,可用于制备SPCS, 但其含有多种危险重金属.因此,本研究将CRT玻璃粉作为胶凝材料,CRT玻璃砂作为骨料,应用到SPCS与OPC中,并对比了2种胶凝体系对重金属的固化效果以及长期性能.结果表明,相比于OPC体系,SPCS体系具有更优异的重金属固化效果,同时也能更显著地抑制碱骨料反应.
二氧化碳排放引起的气候变化,引起了全世界的广泛关注.在建筑业中,普通硅酸盐水泥(OPC)的生产是碳排放的最大贡献
综上,本文将CRT玻璃粉添加到SPCS与OPC胶凝体系中,探究这2种胶凝体系对CRT玻璃粉中重金属的固化效果,并揭示其固化机理.
粒状高炉矿渣(slag,S95)来自于广东韶钢.CRT玻璃(面板部分)来自香港废弃电子设备回收商,其中部分被破碎成与河砂粒度分布相似的细颗粒,标记为CRTGS,作为细骨料使用;部分被研磨成粉末,标记为CRTGP,作为辅助性胶凝材料使用.OPC (CEM1, 52.5)来自于香港青洲英泥.磷石膏(PG)来自贵州省磷酸生产工厂,在与其他胶凝材料混合之前进行了预处理,即:将PG与OPC以8.8∶1.0的质量比均匀混合,然后加入自来水并在实验室环境中静置18

图1 胶凝材料与骨料的粒径分布
Fig.1 Particle size distributions of cementitious materials and aggregates
Material | Al2O3 | BaO | CaO | Fe2O3 | K2O | MgO | Na2O | PbO | P2O5 | Sb2O3 | SiO2 | SO3 | SrO | ZrO2 |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
PG | 0.38 | — | 42.00 | 0.38 | 0.16 | 0.21 | — | — | 1.00 | — | 3.30 | 52.00 | 0.09 | — |
Slag | 13.90 | — | 44.90 | 0.33 | 0.70 | 4.39 | — | — | 0.10 | — | 31.60 | 2.70 | 0.09 | 0.04 |
OPC | 4.10 | — | 67.00 | 2.80 | 0.76 | 1.30 | — | — | — | — | 19.00 | 5.00 | — | — |
CRT | 2.50 | 9.50 | 0.85 | 0.16 | 8.50 | 0.40 | 8.70 | 1.70 | — | 0.35 | 54.00 | — | 10.00 | 2.10 |
将辅助性胶凝材料(slag、CRTGP或经OPC预处理的PG)、骨料(CRTGS与RS的不同比例)、Na2SiO3(碱性活化剂,含量为1%)混合来制备砂浆.砂浆的配合比如
Specimen | Water | Slag | PG | OPC | Activator | CRTGS | RS |
---|---|---|---|---|---|---|---|
SPCSG0S100 | 40.0 | 80.0 | 20.0 | 2.3 | 1.0 | 0 | 200.0 |
SPCSG25S75 | 40.0 | 80.0 | 20.0 | 2.3 | 1.0 | 50.0 | 150.0 |
SPCSG50S50 | 40.0 | 80.0 | 20.0 | 2.3 | 1.0 | 100.0 | 100.0 |
SPCSG75S25 | 40.0 | 80.0 | 20.0 | 2.3 | 1.0 | 150.0 | 50.0 |
SPCSG100S0 | 40.0 | 80.0 | 20.0 | 2.3 | 1.0 | 200.0 | 0 |
OPCG50S50 | 50.0 | 0 | 0 | 100.0 | 0 | 100.0 | 100.0 |
Specimen | OPC | Slag | PG | CRTGP | Activator | Water |
---|---|---|---|---|---|---|
SPCS | 80 | 20 | 1 | 40 | ||
SPCSC30 | 56 | 20 | 24 | 1 | 40 | |
OPC | 100 | 50 | ||||
OPCC30 | 76 | 24 | 50 |
SPCS体系砂浆试块(40 mm×40 mm×40 mm)在3、7、28 d养护((20±2) ℃、相对湿度95%)龄期的抗压强度依据BS EN 12390‑3:2009 Testing Handened Concrete.Compressive Strength of Test Specimens,由Matest 3 000 kN型压力机测得,测试时加载速度设置为0.6 MPa/s,结果取3个平行试块的平均值.
在模具中标准养护((20±2) ℃、相对湿度95%)2 d后,将砂浆棒(25 mm×25 mm×285 mm)脱模,随后立即装入密封塑料袋中再养护((20±2) ℃、相对湿度95%)4 d.之后将它们放置在80 ℃的水浴中浸泡1 d,取出后测得砂浆棒的长度作为初始长度.根据ASTM C1260‑7: Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar‑Bar Method),将砂浆棒在加热的碱性溶液(80 °C)中浸泡14 d后,记录砂浆棒的长度变化.
砂浆棒(25 mm×25 mm×285 mm)在模具中固化2 d((20±2) ℃、相对湿度95%)后脱模,然后在25 ℃的水浴中浸泡5 d,取出后测得砂浆棒的长度作为初始长度.根据ASTM C490: Standard Practice for Use of Apparatus for the Determination of Length Change of Hardened Cement Paste, Mortar, and Concrete,使用比长仪(精度为0.001 mm)测量了砂浆棒从0 d到28 d((20±2) ℃、相对湿度50%)的长度,同时记录砂浆棒在干燥阶段的质量变化.
使用带有Cu Kα辐射源(λ=0.154 nm)的XRD (Rigaku Smart‑Lab)进行测试.在45 kV电压和200 mA的电流下操作,扫描范围为5°到70°,扫描速率为5(°)/min.使用ZnO作为XRD的内标物,测试时取待测样品质量10%的ZnO与样品均匀混合,以实现对晶相和非晶相相对含量的标定.通过定量X射线衍射法分析以获得SPCSC30和OPCC30净浆中各个组分的质量分数.
使用压汞孔隙率计(MIP,Micromeritics AutoPore V 9600 系列)对SPCS和OPC砂浆(在(20±2) ℃、相对湿度95%条件下养护28 d后)的孔隙结构进行测量.待测样品为抗压强度试验后收集的破碎砂浆颗粒,并在乙醇中浸泡7 d来终止水化,随后将样品放入40 ℃的真空烘箱中干燥直至恒重,最后进行MIP测试.
进行重金属毒性浸出测试(TCLP)测试是为了对比分析2种胶凝体系对CRT玻璃粉中重金属的固化效果.在制备TCLP提取液的过程中,首先用去离子水将5.7 mL的冰醋酸稀释至1 000.0 mL,确保溶液的pH值精确控制在(2.88 ± 0.05)的范围内
为了明析CRT玻璃粉部分替代胶凝材料对SPCS和OPC净浆水化的影响,通过XRD测试了CRT玻璃粉30%替代率下,SPCSC30和OPCC30硬化浆体的物相组成,其XRD测试结果见

图2 SPCSC30与OPCC30的XRD图谱
Fig.2 XRD patterns of SPCSC30 and OPCC30
Specimen | Calcite | Ettringite | Gypsum | Portlandite | Quartz | Zincite | Amorphous phase |
---|---|---|---|---|---|---|---|
SPCSC30 | 8.50 | 8.20 | 10.00 | 73.30 | |||
OPCC30 | 13.00 | 0.03 | 0.90 | 8.10 | 2.10 | 10.00 | 65.87 |
SPCSG50S50和OPCG50S50砂浆在养护28 d后的孔经分布曲线如

图3 SPCSG50S50与OPCG50S50的孔径分布曲线
Fig.3 Pore diameter distribution curves of SPCSG50S50 and OPCG50S50
Specimen | d<4.5 nm | 4.5 nm≤d<50.0 nm | 50.0 nm≤d<100.0 nm | d>100.0 nm |
---|---|---|---|---|
SPCSG50S50 | 0.013 42 (13.9%) | 0.051 88 (53.5%) | 0.002 74 (2.8%) | 0.028 84 (29.8%) |
OPCG50S50 | 0 (0%) | 0.011 32 (13.0%) | 0.019 93 (22.8%) | 0.056 09 (64.2%) |
根据研
为了探究CRT玻璃骨料(CRTGS)对OPC和SPCS砂浆抗压强度的影响,通过调整CRTGS对河砂的取代率,测试了不同取代率下OPC与SPCS砂浆的抗压强度,结果见

图4 SPCS与OPC体系使用CRT骨料后的抗压强度
Fig.4 Compressive strength of SPCS and OPC systems after using CRT aggregate
为了研究CRTGS对OPC和SPCS体系干燥收缩的影响,通过在这2种体系中加入不同质量的CRTGS,测试2种砂浆的干燥收缩与水分损失,结果见

图5 SPCS与OPC体系的干燥收缩与水分损失
Fig.5 Drying shrinkage and mass loss of SPCS and OPC
此外,28 d时SPCSG50S50的干燥收缩比OPCG50S50高约0.6倍.不同于骨料对样品干燥收缩的影响,这2个样品的收缩差异主要来自于胶凝体系的不同,即不同净浆的孔隙结构是造成干缩差异的主要原因.研

图6 SPCS与OPC砂浆的碱骨料膨胀
Fig.6 ASR expansion of SPCS and OPC mortars
CRT玻璃粉(CRTGP)中的主要有毒金属包括Ba、Pb和Sr,它们可以通过渗滤液对环境造成危害.为了对比探究OPC和SPCS胶凝体系对CRT玻璃粉中重金属的固化效果,通过模拟真实环境, 对SPCSC30、OPCC30和CRTGP样品进行TCLP测试,结果见

图7 SPCS与OPC体系的TCLP浸出结果
Fig.7 TCLP results of SPCS and OPC
总体而言,SPCS体系表现出优异的重金属固化效果,尤其是对于CRTGP中的Ba和Sr.可见,该新型低碳胶凝材料在实现多种固废循环再生的同
(1)与普通硅酸盐水泥(OPC)体系相比,超硫水泥(SPCS)体系富含硫酸盐矿物相(如钙矾石),且具有更大比例的微孔和介孔,及更小比例的毛细孔.
(2)由于火山灰反应产物和重金属沉淀在骨料周围的填充效应,SPCS砂浆内的界面过渡区性能得以提升,使得阴极射线管(CRT)玻璃骨料替代河砂后28 d的抗压强度略有增加.
(3)使用CRT玻璃骨料完全代替河砂,SPCS浆体的干燥收缩降低了近34%.但与OPC砂浆相比,SPCS砂浆由于介孔体积较大,仍具有较大的干燥收缩.
(4)完全使用 CRT玻璃骨料替代河砂,SPCS砂浆在碱性环境中的ASR膨胀可以忽略不计.
(5)相比于OPC体系,SPCS体系含有大量的钙矾石,可以为有害金属提供更多的阳离子交换位点;同时SPCS体系还存在较多未反应的石膏,可将有毒金属离子转化为硫酸盐沉淀,使得低碳SPCS具有更加优异的重金属固化能力.
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