抗裂高性能混凝土的制备与性能研究

混凝土的开裂问题一直是工程上一道亟待解决的难题。为改善混凝土工作性能,降低水化放热量,增强其抗裂性能,本文通过试验,对不同粉煤灰掺量的混凝土的各项性能进行对比研究,包括力学性能、热学性能和长期性能,比较分析不同粉煤灰掺量下混凝土的各项性能差异。结果表明,随粉煤灰掺量增加,混凝土呈现出强度前期降低后期迅速增长的趋势,当粉煤灰掺量达到50%时,与未掺粉煤灰的试件相比,其7 d抗压强度降低了40.3%,60 d强度较7 d强度增长了53.9%;粉煤灰的加入明显地降低了胶凝体系的放热速率,粉煤灰掺量为50%的胶凝材料7 d水化放热量为171 J/g,较纯水泥的放热量降低了40.3%;在水胶比固定的情况下,粉煤灰的掺入可以降低混凝土的收缩率,粉煤灰掺量为30%时对混凝土的减缩效果最好。

SAP对再生混凝土的抗裂性能影响研究

收缩开裂是困扰再生混凝土性能的突出问题之一,探讨掺入超强吸水树脂(SAP)对于再生混凝土的抗裂性能的影响。通过平板抗裂试验研究了不同再生骨料取代率(0、50%、100%)、不同SAP掺量(0、0.1%、0.2%、0.4%)对再生混凝土抗裂性能的影响。采用扫描电镜(SEM)试验对3、28 d龄期下的50%再生骨料替代率的SAP再生混凝土进行了微观分析,探讨了SAP对再生混凝土的阻裂机理。试验结果表明:掺入SAP可有效缓解再生混凝土出现的开裂现象。当SAP掺量为0.2%时,平均开裂面积减小了39.06%,单位面积上的总开裂面积减少了63.62%,效果最佳。掺入SAP后的水泥水化程度有所提高,提高了再生混凝土的内部湿度,改善再生混凝土内部的结构,提高其内部的致密性,提高了再生混凝土的抗裂性能。

非洲磨细天然火山灰对混凝土收缩抗裂性能的影响研究

研究两种非洲磨细天然火山灰材料单掺以及与粉煤灰复掺对混凝土收缩抗裂性能的影响。结果表明:磨细凝灰岩增大了混凝土的早期收缩,而磨细火山渣可以有效降低混凝土早期收缩;掺加两种磨细天然火山灰均能降低混凝土长期收缩和水化温升;两种天然火山灰和粉煤灰均对混凝土抗裂性能有所提升,提升效果方面粉煤灰大于磨细火山渣,磨细火山灰大于磨细凝灰岩,磨细火山渣与粉煤灰复掺与单掺等量粉煤灰对混凝土抗裂性能的改善效果相当。

Influence of superplasticizers on the early-age crack resistance of concrete

In order to improve the early-age cracking resistance of concrete, different types of superplasticizers are used. Two types of polycarboxlic salt/acid superplasticizers and one retarding naphthalene superplasticizer are selected to investigate the influence of superplasticizers on the early-age cracking resistance of the concrete by using the slab test and the temperature-stress test. The results show that the polycarboxlic salt/acid superplasticizer cannot always improve the cracking resistance capacity of the concrete compared with the naphthalene superplasticizer, which is related to the chemical structure of the polycarboxlic salt/acid superplasticizer. High plastic tensile strength and dynamic elastic modulus at the early stage are beneficial to avoid cracking, and low hydration heat is also helpful. The evolutions of the drying shrilakage stress and the hydration heat temperature stress varying with time can be comprehensively evaluated by means of the slab test and the temperature stress test.