摘要
系统研究了以NaOH、水玻璃以及NaOH复掺Na2CO3为激发剂,激发矿渣、粉煤灰、矿渣/粉煤灰和矿渣/水泥4种胶凝体系的凝结时间和7 d抗压强度变化规律,获得了凝结时间与掺量变化公式及早期抗压强度预测公式.结果表明:单一NaOH或水玻璃激发矿渣条件下,掺入少量粉煤灰、水泥对改善复掺体系凝结时间的效果不显著,并且均会降低早期抗压强度;采用NaOH/Na2CO3复合激发剂后,能够有效延长体系凝结时间,在一定程度上提高体系抗压强度.针对NaOH/Na2CO3复掺激发矿渣/水泥体系凝结时间和抗压强度出现“不增却减”的现象,深入讨论了掺NaOH/Na2CO3复合激发剂的作用机理.
碱激发胶凝材料绿色环保,在替代传统水泥材料方面将起到非常重要的作用.然而,碱激发胶凝材料面临的问题是:因胶凝材料体系不同而导致其凝结时间差异很大,没有统一的规律,阻碍了其大规模推广及应用.Zivic
本文以NaOH和水玻璃作为激发剂,矿渣、粉煤灰及水泥作为胶凝材料,Na2CO3作为缓凝剂,研究了各种碱激发材料体系的凝结时间和抗压强度变化规律,得出凝结时间与掺量变化公式和早期抗压强度预测公式,可为碱激发混凝土的材料设计与调控提供依据.
矿渣(S):比表面积450
Material | SiO2 | Al2O3 | Fe2O3 | CaO | MgO | K2O | Others |
---|---|---|---|---|---|---|---|
Slag | 34.11 | 15.32 | 0.73 | 37.25 | 8.49 | 0.37 | 3.73 |
Fly ash Cement |
55.71 20.11 |
32.79 4.25 |
4.43 3.23 |
2.65 64.85 |
0.24 0.88 |
1.54 0.67 |
2.64 6.01 |
碱性激发剂:水玻璃(WG),模数为1.0;分析纯NaOH(NH),纯度为99%;分析纯Na2CO3(NC).
本试验均控制水胶比为0.35,碱掺量为6%,室温为20 ℃.制备NaOH和水玻璃激发的矿渣及粉煤灰单一胶凝材料体系.同时,制备矿渣/粉煤灰与矿渣/水泥复合胶凝材料体系,其中粉煤灰或水泥按照总胶凝材料质量的20%、40%、60%、80%替代矿渣,分别用NaOH和水玻璃激发.
另外,以30%的Na2CO3替代NaOH,制备成NaOH/Na2CO3复合激发剂,掺入100%矿渣、80%矿渣+20%粉煤灰和80%矿渣+20%水泥3个胶凝体系.Na2CO3在20 ℃时溶解度为22 g,在本文水胶比0.35条件下,其提供的最大碱掺量为3.7%(<6.0%),故不单独作为激发剂使用.(注:碱掺量为总Na2O与总胶凝材料质量之比;Na2CO3掺量为其提供的Na2O和总Na2O质量之比)
试件编号方式为“激发剂-胶凝材料”,如NH‑S/FA代表NaOH激发的矿渣/粉煤灰体系.
Material | Activator | Setting time/min | Compressive strength/MPa | ||
---|---|---|---|---|---|
Initial | Final | 3 d | 7 d | ||
Slag | Waterglass | 25 | 38 | 52.4 | 62.9 |
Slag | NaOH | 33 | 41 | 35.6 | 47.9 |
Fly ash | Waterglass | 744 | 902 | 0.6 | 0.7 |
Fly ash | NaOH | 2 395 | 2 508 | — | 0.5 |
Cement | 245 | 273 | 56.1 | 67.4 |
碱激发矿渣/粉煤灰净浆性能如

图1 碱激发矿渣/粉煤灰净浆凝结时间与早期强度
Fig.1 Setting time and early age compressive strength of alkali‑activated slag/fly ash paste
以粉煤灰掺量wFA=60%为分隔点,拟合得到碱激发矿渣/粉煤灰体系凝结时间与粉煤灰掺量的关系曲线,见式(
(1) |
(2) |
(3) |
(4) |
式中:、分别为NaOH激发矿渣/粉煤灰体系的初凝、终凝时间,min;、为水玻璃激发矿渣/粉煤灰体系的初凝、终凝时间,min.
由
(5) |
(6) |
式中:为NaOH激发矿渣/粉煤灰体系7 d抗压强度,MPa;为水玻璃激发矿渣/粉煤灰体系7 d抗压强度,MPa.
根据式(
由水泥与矿渣混合制备的碱激发矿渣/水泥体系性能如

图2 碱激发矿渣/水泥净浆凝结时间与早期强度
Fig.2 Setting time and early age compressive strength of alkali activated slag/cement paste
拟合得到碱激发矿渣/水泥体系凝结时间与水泥掺量的关系曲线,见式(
(7) |
(8) |
(9) |
(10) |
式中:、分别为NaOH激发矿渣/水泥体系的初凝、终凝时间,min;、为水玻璃激发矿渣/水泥体系的初凝、终凝时间,min.
由
(11) |
(12) |
式中:为NaOH激发矿渣/水泥体系7 d抗压强度,MPa;为水玻璃激发矿渣/水泥体系7 d抗压强度,MPa.
矿渣/水泥复合体系终凝时间均满足规范标准.若只考虑初凝时间要求,根据式(
综上,碱激发矿渣/水泥体系中水泥的掺入能在较小程度上改善NaOH工况下的速凝问题,而对水玻璃工况下无明显改善;水泥的掺入对早期抗压强度有劣化作用,复合胶凝材料体系强度低于单一激发矿渣和单一水泥净浆的强度.
除了NaOH激发矿渣/水泥体系之外,Na2CO3对碱激发矿渣、碱激发矿渣/粉煤灰和碱激发矿渣/水泥这3种胶凝体系都起到缓凝的作用;并且Na2CO3的掺入使得各体系早期抗压强度呈现不同程度的增加,如
Material | Activator | Setting time/min | Compressive strength/MPa | ||
---|---|---|---|---|---|
Initial | Final | 3 d | 7 d | ||
100%S | WG | 25 | 38 | 52.4 | 62.9 |
WG+NC | 32 | 64 | 56.7 | 71.1 | |
NH | 33 | 41 | 35.6 | 47.9 | |
NH+NC | 58 | 76 | 38.7 | 53.6 | |
80%S+20%FA | WG | 29 | 39 | 45.3 | 51.7 |
WG+NC | 56 | 108 | 47.5 | 54.6 | |
NH | 34 | 43 | 29.1 | 33.6 | |
NH+NC | 183 | 236 | 32.5 | 36.1 | |
80%S+20%C | WG | 18 | 35 | 51.1 | 59.2 |
WG+NC | 47 | 103 | 54.6 | 68.7 | |
NH | 55 | 80 | 33.5 | 44.6 | |
NH+NC | 46 | 65 | 29.1 | 36.1 |
另外,当掺入Na2CO3后,NaOH激发矿渣/水泥的凝结时间和抗压强度都出现“不增却减”的现象.具体原因将在下文进一步讨论.
NaOH激发矿渣24 h后,体系产物有C‑A‑S‑H、C‑S‑H和水滑石
Na2CO3复合激发剂在矿渣/粉煤灰胶凝体系中的作用机理如

图3 Na2CO3复合激发剂的作用机理
Fig.3 Action mechanism of compound activator with Na2CO3
针对掺入Na2CO3复合激发剂后NaOH激发矿渣/水泥胶凝体系凝结时间与抗压强度“不增却减”的现象(
(1)碱激发矿渣胶凝材料体系凝结时间最快,碱激发粉煤灰胶凝材料体系凝结时间最慢.对于矿渣/粉煤灰复合胶凝材料体系,凝结时间随着粉煤灰掺量的增大而增加,但当粉煤灰掺量小于60%时,凝结时间主要受矿渣反应的影响;早期抗压强度变化与粉煤灰掺量呈线性关系,随着粉煤灰掺量的增加而下降,在水玻璃激发工况下的下降速率更快.
(2)碱激发矿渣/水泥体系中水泥掺量的增加在较小程度上延长了凝结时间,在水玻璃激发工况下体系凝结时间仍然快于规范要求.由于碱性环境下矿渣反应和水泥水化的相互影响,碱激发矿渣/水泥体系抗压强度低于碱激发纯矿渣或单一水泥水化时的抗压强度.
(3)相比于单一激发剂,NaOH与Na2CO3复掺激发80%矿渣+20%粉煤灰和80%矿渣+20%水泥复合胶凝材料时,凝结时间延长,抗压强度增大.
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