摘要
为了解决建筑固废资源化利用的技术难题,研究了钛石膏-矿渣浆体(T‑S浆体)强化砖混再生粗集料(BCRCA)的作用机理,比较了负压强化与传统搅拌裹附强化效果的优劣,分析了T‑S浆体强化水泥稳定碎石混合料无侧限抗压强度和劈裂强度的变化.结果表明:T‑S浆体可以产生C‑S‑H凝胶和钙矾石微膨胀体,填充粗集料的孔隙;负压强化BCRCA的压碎值达到27.5%,吸水率降低至6.6%,表观密度提高至2.678 g/c
随着中国城市建设的发展,建筑固废总量已占到城市垃圾总量的30%~40
采用化学浆液或溶液浸泡、渗透结晶改性、纳米技术改性和碳化处理等方
现阶段缺少效果明显、成本不高和简单易控的强化材料,也没有较好的强化处理方式.传统搅拌和浸泡强化并不能满足使用要求,已经成为制约强化再生集料广泛应用的瓶颈.从再生集料的强化方式与材料入手,选用一种成本低廉、效果优异的强化材料对砖混再生粗集料(BCRCA)进行强化,并提出一种新的负压强化方式,研究其强度的变化规律,可以解决建筑垃圾资源化利用的问题,在极大程度上促进BCRCA再生利用技术的推广.
水泥采用山水集团供应的P·O 42.5水泥,性能如
采用课题组自主研发的小型负压强化设

图1 钛石膏的XRD图谱
Fig.1 XRD pattern of titanium gypsum

图2 矿渣的XRD图谱
Fig.2 XRD pattern of slag
在反应过程中钛石膏会分离出和C
第1步:.
第2步:
. |
第3步:2H2O→2{Ca3A1(OH)612H2O
前期研究表

图3 不同养护龄期下T‑S浆体的微观形貌
Fig.3 Microstructure of T‑S paste with different curing ages
首先,以0.1为间隔,确定T‑S浆体水胶比mW/mB为1.3~1.8,浆体裹附效果如

图4 钛石膏-矿渣浆体的裹附效果
Fig.4 Adhesion effect of titanium gypsum slag slurry
将T‑S浆体所能浸入深度与孔隙总深度的比值定义为灌入饱和度,以此来表征T‑S浆体灌入孔隙的程度.利用CT扫描技术对T‑S浆体强化BCRCA前后的孔隙充盈情况和孔隙特征进行观察,结果如图

图5 强化材料灌入程度示意图
Fig.5 Schematic diagram of filling degree of strengthening materials

图6 强化BCRCA的孔隙特征扫描图
Fig.6 Scanning graph of pore characteristics of strengthening BCRCA

图7 BCRCA各项性能指标的变化规律
Fig.7 Variation law of each performance index of BCRCA
(1)强化BCRCA的吸水率随着水胶比的增大呈先减小后增大的趋势.分析可知,水胶比变化反映了强化浆体稠度的变化,过稠或过稀都会降低浆体的裹附效果.水胶比为1.5时,BCRCA易于被T‑S浆体包裹.当采用搅拌裹附强化方式时,随着搅拌时间的延长,吸水率不断降低,使更多的T‑S浆体浸入孔隙中,从而获得了较好的强化效果.在搅拌60 min后强化效果最佳,吸水率降至7.2%.当采用负压强化方式时,T‑S浆体能够更好地填充集料孔隙,并且反应生成钙矾石晶体和C‑S‑H凝胶,使集料更加密实,从而有效提高集料的性能,使吸水率降至6.6%,较未强化时降低32.6%.
(2)当水胶比为1.5时,强化BCRCA的表观密度达到最大值.这是由于水胶比的不同,导致浆体的稠度和流动性不同,使填充程度出现差异.搅拌时间的影响较弱,当搅拌60 min时,浆体已经开始趋向于初凝状态;搅拌40 min后,BCRCA的表观密度已达到2.673 g/c
(3)强化BCRCA的压碎值随着水胶比的增大而减小.当水胶比为1.7时,强化BCRCA的压碎值达到最优状态,搅拌40、60 min时的压碎值约为28.0%;经过负压强化后的压碎值降低至27.5%,与原始状态下的32.9%相比,降低了16.4%.但是,与搅拌裹附强化相比,负压强化BCRCA的吸水率有所减小.当选择水胶比为1.5时,负压强化BCRCA的吸水率最小、表观密度最大,并且压碎值也变化不大.因此,在负压强化方式下,最优水胶比为1.5.
从强化方式和孔隙特征2方面对灌入饱和度的变化规律进行分析,结果如
(1)从强化方式上来看,当采取传统搅拌裹附强化方式时,BCRCA的灌入饱和度随着搅拌时间的延长而增大,但是连通孔隙的灌入饱和度仅为15.2%,开口孔隙的灌入饱和度为23.4%.经过负压强强化后,BCRCA的灌入饱和度有明显提升,其开口孔隙和连通孔隙的灌入饱和度分别提高至38.3%、27.5%.由此看出,负压强化方式可以有效提高强化材料浆体灌入集料孔隙的程度,从而提升了BCRCA的各项性能指标,使其达到使用条件.
(2)从孔隙特征上来看,BCRCA的开口孔隙灌入饱和度比连通孔隙提升了约25.1%.因为连通孔隙中外部孔隙与内部孔隙的连接通道较为狭窄,T‑S浆体不易进入孔隙内部,从而导致灌入饱和度较差.开口孔隙具有较宽的流通通道,T‑S浆体可以更好地灌入粗集料孔隙中,从而达到密实孔隙的目的.因此,负压强化方式能够更好地强化BCRCA.
级配设计采用4档集料,分别为G1(20~30 mm)、G2(10~20 mm)、G3(5~10 mm)和G4(0~5 mm),筛分试验后调整确定4档集料比例为m(G1)∶m(G2)∶m(G3)∶m(G4)=17∶23∶23∶37,级配如
采用水泥剂量为5%,含水量按8%、9%、10%、11%和12%添加,分别进行击实试验,得到水泥稳定碎石混合料含水量与干密度的关系,结果如

图8 水泥稳定碎石混合料含水量与干密度的关系
Fig.8 Relationship between dry density and water content of cement stabilized stone mixture
(1)在负压强化方式下,当水胶比为1.7时,砖混再生粗集料(BCRCA)的压碎值可降低至27.5%,较未强化时降低16.4%.为了兼顾吸水率与表观密度的影响,选择1.5作为最佳水胶比,此时BCRCA压碎值所受的影响不大,且吸水率、表观密度达到6.6%、2.678 g/c
(2)与传统搅拌裹附强化方式相比,经过负压强化方式强化后,BCRCA开口孔隙和连通孔隙的灌入饱和度分别提高至38.3%、27.5%,并且T‑S浆体能够更好地灌入开口孔隙,其灌入饱和度比连通孔隙提升了25.1%.
(3)强化后的BCRCA用于水泥稳定碎石基层时,其7 d无侧限抗压强度和劈裂强度分别为3.8、0.41 MPa,较未强化时提升了38.5%、36.7%,可以达到较好的强化效果.
(4)BCRCA强化后,水泥稳定碎石混合料的平均疲劳寿命提高了30.8%,抗冲刷性能提升了17.5%,具有较好的耐久性能.
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