摘要
研究了冻融环境中不同掺量和水胶比条件下,活化煤矸石粉(ACGP)对混凝土毛细吸水性能的影响规律;同时结合非饱和毛细理论,建立了活化煤矸石粉混凝土(ACGPC)的相对含水量分布预测模型.结果表明:冻融作用使得ACGPC的累计吸水量及毛细吸水率逐渐增大,抗毛细吸水性能降低,水分侵入深度提高;当ACGP掺量相同时,ACGPC的抗毛细吸水性能随着水胶比的增加而降低;当水胶比一定时,随着ACGP掺量的增加,ACGPC的累计吸水量及毛细吸水率先降后升;ACGP可细化混凝土孔径,当ACGP掺量为20%时效果最为显著.
煤矸石是煤炭开采过程中排放量极大的工业固废物.大量堆积的煤矸石会污染生态环境,危害公共安
工程中多数建筑结构处于非饱和环境中,且水分的传输由扩散和毛细吸收控制,国内外学者针对混凝土的毛细吸水特性进行了大量研究.其中,Zhao
由于目前关于ACGPC的研究集中于活化方式、力学性能及氯离子渗透
水泥(C)采用陕西礼泉海螺水泥公司P·O 42.5普通硅酸盐水泥;细骨料(S)采用灞河粗砂,细度模数为3.2,含泥量小于2%;粗骨料(G)采用普通碎石,粒径为5~25 mm,表观密度为2 871 kg/
SiO2 | Al2O3 | Fe2O3 | CaO | MgO | TiO2 | K2O | IL |
---|---|---|---|---|---|---|---|
45.90 | 16.00 | 4.71 | 0.74 | 1.37 | 0.78 | 3.36 | 21.03 |
基于文献[
ACGP及水泥的粒度分布曲线见

图1 ACGP及水泥的粒度分布曲线
Fig.1 Granularity distribution curves of ACGP and cement

图2 CGP和ACGP的XRD图谱
Fig.2 XRD patterns of CGP and ACGP
本试验ACGPC的砂率取为36%,引气剂掺量为胶凝材料质量的0.03%.ACGPC的配合比及基本性能见
Group No. | Mix proportion/(kg· | Air content (by volume)/% | Slump/mm | 28 d compressive strength /MPa | ||||||
---|---|---|---|---|---|---|---|---|---|---|
W | C | ACGP | S | G | PBS | AOS | ||||
S40C0 | 165 | 413 | 0 | 656 | 1 166 | 4.95 | 0.12 | 5.4 | 184 | 35.9 |
S40C1 | 165 | 371 | 41 | 656 | 1 166 | 4.95 | 0.12 | 5.3 | 203 | 36.6 |
S40C2 | 165 | 330 | 83 | 656 | 1 166 | 4.95 | 0.12 | 5.1 | 190 | 38.0 |
S40C3 | 165 | 289 | 124 | 656 | 1 166 | 4.95 | 0.12 | 4.6 | 176 | 33.0 |
S35C2 | 160 | 366 | 91 | 642 | 1 141 | 6.85 | 0.14 | 4.9 | 185 | 41.6 |
S45C2 | 164 | 292 | 73 | 674 | 1 197 | 3.65 | 0.11 | 5.5 | 195 | 31.2 |
本试验制作2种试件:尺寸为100 mm×100 mm×100 mm的立方体试件,每组各9个;尺寸为100 mm×100 mm×400 mm的棱柱体试件,每组各3个.各组试件均浇筑24 h后脱模,并置于标准养护箱((20±2)℃、相对湿度RH≥95%)中养护至规定龄期.
按照GB/T 50082—2009《普通混凝土长期性能和耐久性能试验方法标准》中的“快冻法”,先将试件在标准养护箱中养护至24 d,再置于水中浸泡4 d后进行冻融循环试验.其中棱柱体试件每冻融循环25次后取出,测试其质量损失率和相对动弹性模量,结果取平均值;立方体试件达到预定冻融循环次数(N)后取出,进行毛细吸水试验及扫描电镜(SEM)和核磁共振(NMR)分析.
毛细吸水试验参照ASTM C1585‑13《Standard test method for measurement of rate of absorption of water by hydraulic cement concretes》进行,每组3个立方体试件,取其平均值作为试验结果.试验前先将试件在60 ℃下干燥至恒重(24 h质量损失率小于0.1%),取出后再使用环氧树脂将其4个侧面进行疏水处理,之后用塑料薄膜密封顶面.试验过程中,试件触水面须浸入水面5 mm以内,分别在试验开始后的0、1、5、10、20、30 min,1、2、3、4、5、6 h,1、2、3、5、6、7、8 d时称量并记录试件质量.试件的累积吸水量(I,mm)和毛细吸水率(S,mm/
(1) |
(2) |
式中:为试件的质量变化,g;A为试件的触水面积,m
图

图3 冻融环境下ACGPC的质量损失率
Fig.3 Mass loss rate of ACGPC in freeze‑thaw environment

图4 冻融环境下ACGPC的相对动弹性模量
Fig.4 Relative dynamic elastic modulus of ACGPC in freeze‑thaw environment
由
由

图5 冻融环境下ACGPC的累计吸水量
Fig.5 Cumulative water absorption of ACGPC in freeze‑thaw environment
由

图6 冻融环境下ACGPC的初始吸水率及二次吸水率
Fig.6 Initial and secondary water absorption of ACGPC in freeze‑thaw environment
由
由
(3) |

图7 S40C0组和S40C2组在不同冻融循环次数下的SEM照片
Fig.7 SEM images of group S40C0 and S40C2 under different freeze‑thaw cycles
由
混凝土的孔结构参数与其毛细吸水性能有很大相关性,本文对冻融循环前后性能最好的S40C2组及对照组S40C0组进行NMR试验.根据NMR原理,由于横向表面弛豫时间(T2s,ms)与孔隙尺寸成正比,引入孔隙形状后的T2可简化
(4) |
式中:ρ2为表面弛豫强度,根据经验,混凝土的ρ2可取为5 nm/ms;r为孔隙半径,μm;F为孔形状系数,本文取为3.
由

图8 S40C2组和S40C0组的孔径分布
Fig.8 Pore diameter distribution of group S40C2 and S40C0
根据吴中伟提出的混凝土孔径划分理

图9 S40C2和S40C0组各孔径的孔隙率及孔径级配
Fig.9 Porosity and pore size gradation of each pore size of group S40C2 and S40C0
一般采用扩展Darcy定律来描述非饱和混凝土的毛细吸水作
(5) |
式中:为混凝土内部的相对含水量;D(θ)为水分扩散系数,采用指数形式表示,其中D0表示饱和状态下的水分扩散系数,参数n与材料性能几乎无关,取值一般为6~
引入Boltzmann变量后,可得到混凝土内部任意时刻(t)的水分渗入深度(x
(6) |
其中
(7) |
(8) |
式(
结合毛细吸水试验测得的S1,建立ACGPC内部θ的预测模型.

图10 S40C2组和S40C0组的相对含水量分布曲线
Fig.10 Relative water content distribution curves of group S40C2 and S40C0
(1)不同冻融循环次数下,掺入活化煤矸石粉(ACGP)后混凝土的抗冻性能和抗毛细吸水性均得到提升,且在ACGP掺量为20%时提升效果最为显著.
(2)活化煤矸石粉混凝土(ACGPC)的累计吸水量变化规律与普通混凝土相似,为2个线性阶段变化趋势,前期吸水速率较高,后期较为缓慢.未冻融时,ACGP以20%掺量加入混凝土后,ACGPC的初始吸水率降低22.70%;当ACGP掺量达到30%,在冻融后期ACGPC的质量损失率较大,抗毛细吸水性能下降严重.
(3)掺入ACGP能够增加ACGPC无害孔占比,减少有害孔,能够显著改善混凝土的孔径级配;冻融循环作用虽然使ACGPC中的少害孔和多害孔有所增加,但后者的增加要远小于普通混凝土,且冻融损伤产生的裂缝较少,使得冻融环境下ACGPC的性能优于普通混凝土.
(4)结合非饱和毛细吸水相关理论,考虑冻融作用和ACGP掺量的影响,通过指数型水分扩散系数,建立了可以有效预测ACGPC内部相对含水量分布的模型,为ACGPC耐久性研究提供一定的理论依据.
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