摘要
为探明石灰岩机制砂在严寒地区应用的合理性,以相对动弹性模量为评价指标,研究了混凝土强度等级、含气量和石粉含量对石灰岩机制砂混凝土抗冻性能的影响规律,采用吸水率和气泡间距系数分析了石灰岩机制砂混凝土冻融破坏原因. 结果表明:高强石灰岩机制砂混凝土具有高抗冻和破坏突发特征,提高混凝体强度等级或引入适量优质气泡是提高石灰岩机制砂混凝土抗冻性能的有效途径;当C30和C60石灰岩机制砂混凝土含气量分别为6.4%和4.4%时,混凝土的抗冻性能最佳;石灰岩石粉对混凝土性能有正、负双重效应,其含量控制在10.0%以内对混凝土抗冻性能、力学性能和工作性能有利.
采用机制砂替代河砂,将其作为混凝土骨料逐渐成为工程材料绿色发展的主流趋势. 石灰岩凭借储量丰富、可加工性良好和矿物成分单一等优
国内外学者开展了石灰岩机制砂混凝土抗冻性能研究.如 Li
混凝土的吸水率能够衡量其内部开孔孔隙中可冻水的含
水泥(C)为P·O 42.5普通硅酸盐水泥,性能指标满足GB 175—2007《通用硅酸盐水泥》要求;粉煤灰(FA)为F类Ⅰ级粉煤灰;粗骨料为5~20 mm连续级配碎石(G);减水剂(SP)为减水率32%、固含量28.25%的聚羧酸系高性能减水剂;引气剂(AE)为减水率7%、含气量4.1%的松香树脂类引气剂;水(W)为自来水;细骨料为石灰岩机制砂(LS)和河砂(RS),主要性能如
No. | Apparent density/(g·c | Soundness/% | Crushing index/% | MB value/% | Water absorption(by mass)/% | 14 d expansivity/% | w(mica)/% | Modulus of fineness |
---|---|---|---|---|---|---|---|---|
LS | 2.70 | 1 | 11 | 1.0 | 1.0 | 0.07 | 0 | 2.8 |
RS | 2.57 | 2 | — | — | 0.8 | 0.01 | 0.1 | 2.7 |

图1 石灰岩石粉的粒度分布
Fig.1 Particle size distribution of limestone powder
参照JGJ 55—2011《普通混凝土配合比设计规程》,设计C30、C45和C60石灰岩机制砂混凝土配合比,见
Strength grade | Water‑binder ratio | Mix proportion/(kg· | Slump/mm | Air content(by volume)/% | ||||||
---|---|---|---|---|---|---|---|---|---|---|
C | FA | LS or RS | G | W | SP | AE | ||||
C30 | 0.50 | 280.00 | 70.00 | 832.00 | 1 081.00 | 175.00 | 1.50 | 0.11 | 175 | 4.6 |
C45 | 0.40 | 320.00 | 80.00 | 805.00 | 1 085.00 | 160.00 | 1.75 | 0.21 | 170 | 4.6 |
C60 | 0.28 | 384.00 | 96.00 | 734.00 | 1 101.00 | 135.00 | 3.40 | 0.27 | 185 | 4.4 |
Note: The limestone powder content of manufactured sand is 7.5%(by mass).
以
制备不同石粉含量石灰石机制砂混凝土时,将C30和C60混凝土中的石灰岩机制砂石粉含量(以石灰岩机制砂质量计)设计为0%、5.0%、7.5%、10.0%、12.5%和15.0%,并采用河砂制备对照组混凝土RSC30和RSC60.
(1)抗冻性能
依据GB/T 50082—2009《普通混凝土长期性能和耐久性能试验方法标准》进行快冻法试验. 将试件养护至28 d龄期后,先测试其初始动弹性模量和质量,每冻融循环25次后再测试其相对动弹性模量和质量损失率;当试件相对动弹性模量下降至60%或质量损失率达到5%时停止试验,并记录抗冻循环次数及质量损失率.
(2)吸水率
首先将边长为100 mm的立方体试件养护至28 d;然后在60 ℃下烘干至恒重(质量记为m1);接着将其完全浸没在水中,保持水面至少高出试件25 mm;当试件分别浸泡0.5、1.0、3.0、14.0、24.0、36.0、48.0 h后,将其取出并擦干表面水分,迅速称重(质量记为mi). 不同浸泡时间(i)条件下混凝土的吸水率(A)按
(1) |
(3)气泡间距系数
参照 TB/T 3275—2018《铁路混凝土》,首先将标准养护28 d龄期的试件切割成边长为100 mm、厚度为20 mm的棱柱体试件,并将其表面抛光;然后采用黑色颜料标记骨料和浆体,采用白色颜料标记孔隙;最后将处理后的试件置于RapidAir自动图像分析仪中,测试其气泡间距系数.

图2 石灰岩机制砂混凝土抗压强度
Fig.2 Compressive strength of limestone manufactured sand concretes

图3 不同强度等级石灰岩机制砂混凝土抗冻性能
Fig.3 Frost resistance of limestone manufactured sand concrete with different strength grades
按照损伤理论观点,材料在循环荷载或长期荷载作用下,一般会经历从无损伤到形成微裂纹损伤过程和裂纹拓展形成宏观破坏过程2个阶

图4 石灰岩机制砂混凝土P‑Δ曲线
Fig.4 P‑Δ curves of limestone manufactured sand concretes

图5 不同强度等级石灰岩机制砂混凝土的吸水率
Fig.5 Water absorption of limestone manufactured sand concretes with different strength grades

图6 不同强度等级石灰岩机制砂混凝土的气泡间距系数
Fig.6 Bubble spacing coefficient of limestone manufactured sand concretes with different strength grades

图7 不同含气量石灰岩机制砂混凝土的抗压强度
Fig.7 Compressive strength of limestone manufactured sand concretes with different air contents

图8 不同含气量石灰岩机制砂混凝土的抗冻性能
Fig.8 Frost resistance of limestone manufactured sand concretes with different air contents

图9 不同含气量石灰石机制砂混凝土的48 h吸水率
Fig.9 48 h water absorption of limestone manufactured sand concretes with different air contents

图10 不同含气量石灰石机制砂混凝土的气泡间距系数
Fig.10 Bubble spacing coefficient of limestone manufactured sand concretes with different air contents

图11 不同石粉含量机制砂混凝土的工作性能
Fig.11 Workability of manufactured sand concretes with different limestone powder contents

图12 不同石粉含量机制砂混凝土的抗压强度
Fig.12 Compressive strength of manufactured sand concretes with different limestone powder contents

图13 不同石粉含量石灰石机制砂混凝土的抗冻性能
Fig.13 Frost resistance of limestone manufactured sand concrete with different limestone powder contents

图14 不同石粉含量石灰石机制砂混凝土的48 h吸水率
Fig.14 48 h water absorption of limestone manufactured sand concretes with different limestone powder contents

图15 不同石粉含量石灰石机制砂混凝土的气泡间距系数
Fig.15 Bubble spacing coefficient of limestone manufacturedsand concretes with different powder contents
(1)通过提高混凝土强度等级、适当引气以及控制石粉含量能够制备出适用于严寒地区抗冻要求的石灰岩机制砂混凝土.
(2)相同含气量条件下,随着混凝土强度等级的提高,石灰石机制砂混凝土抗冻性提高.高强混凝土基体脆性大,具有冻融破坏突发特征.
(3)引入优质气泡可以提高石灰岩机制砂混凝土的含气量,降低气泡间距系数,缓解混凝土结冰冻胀应力,提升混凝土抗冻性能. C30和C60混凝土最佳抗冻性能的含气量分别为6.4%和4.4%.
(4)石灰岩石粉在机制砂混凝土中具有正、负双重效应. 当石粉含量为10.0%时,C30和C60石灰岩机制砂混凝土的抗冻性能最好;综合考虑抗冻性能、力学性能和工作性能,石灰岩机制砂石粉含量以小于10.0%为宜.
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