纳米SiO_2对钢纤维混凝土高温抗压性能的影响及微观分析

Influence and microanalysis of nano SiO_2 on high-temperature compressive properties of steel fiber reinforced concrete(SFRC)

研究了普通混凝土(NC)、钢纤维增强混凝土(SFRC)、掺纳米SiO_2的普通混凝土(NNC)、掺纳米SiO_2的钢纤维混凝土(NSFC)四种混凝土高温时和高温后抗压性能试验,对不同温度下的微观结构进行了SEM分析,对基体相结构进行了XRD分析。结果表明,四种混凝土的高温后立方体抗压强度在400℃时达到最大值。其中NSFC的抗压强度最高,为88.46 MPa,比同温下的SFRC提高21.68%,比NC提高25.96%。四种混凝土高温时抗压强度在200℃时就达到峰值。200℃时,NSFC的抗压强度为77.45 MPa,分别是同温度时SFRC、NNC、NC的1.13、1.21、1.34倍。纳米SiO_2可与水泥水化产物Ca(OH)2发生二次水化反应,降低Ca(OH)_2含量和细化Ca(OH)_2晶体,把对强度不利的Ca(OH)_2转化为C-S-H凝胶,提高基体密实度。因此加入纳米SiO_2可明显提高混凝土的高温抗压强度,特别是对提高钢纤维混凝土的抗压强度具有显著作用。

It investigated the compressive strength of the normal concrete （NC）, the steel fiber reinforced concrete （SFRC）, the nano normal concret （NNC） and the nano-steel fiber reinforced concrete（NSFC ） at the high temperature and after the high temperature.On the other hand, Scanning Electron Microscopy （SEM） and X-ray diffraction （XRD） were used to analyze Micro-Structure and Matrix phase structure at different temperatures.Results presented that that within 400 ℃ ,the compressive strength ofNSFC, SFRC ,NNC and NC after high temperature were improved as temperature increased, reaching a maximum value at 400 ℃ .The compressive strength of NSFC among the four types of concrete was the maximum,and it was 88.46 MPa which was 21.68% higher than that of SFRC and 25.96% higher than that of NC under the same temperature.The peak values of compressive strength of four types of concrete under high temperature appeared under 200 ℃ .The compressive strength of NSFC was 77.45 MPa under 200 ℃, respectively being 1.13,1.21 and 1.34 times of those of SFRC, NNC and NC.Nano SiO2 could go through secondary hydration reaction with cement hydration product Ca （OH）2 so as to reduce Ca （ OH ）2 content and refine Ca （ OH ）2 crystals, transform Ca （ OH ）2 having adverse effect on strength into C-S-H gels and improve struc- tural compactness.Therefore,addition of nano SiO2 could obviously improve normal-temperature and high-temperature compressive strengths of the concrete, and it especially played a significantly role in improving compressive strength of SFRC.