养护条件对UHPC强度和毛细吸水性的影响

Effect of curing condition on mechanical strength and capillary water absorption of UHPC

为优化超高性能混凝土(UHPC)预制构件养护工艺,研究了不同养护条件对UHPC强度和毛细吸水性的影响,并采用孔结构测试、热重分析和扫描电镜观察,对其机理进行了分析.结果表明:热养护显著提高了UHPC的7 d强度,这与加速火山灰反应有关,但高温和干热养护对其后期强度增大不利,甚至出现约3%的强度倒缩;不论何种养护,UHPC总体均具有较低的毛细吸水性,毛细吸水系数随试件吸水时间和养护龄期增长而显著降低,干热养护试件的毛细吸水性高于其他养护条件;从综合性能考虑,干热养护温度宜控制在100℃以下,超过150℃会显著增大UHPC的总孔和大孔孔隙率,并增大毛细吸水性.电镜观察到热养护试件内部存有微裂纹,而钢纤维可以抑制周围水化产物微裂纹的发生.

In order to optimize the curing process of ultra-high performance concrete(UHPC)prefabricated components,the effect of different curing conditions on mechanical strength and capillary water absorption of UHPC was investigated,and the mechanism was analyzed by pore structure test,thermogravimetric analysis and scanning electron microscope.Test results indicate that,heat curing regime has a very significant increase on 7 day mechanical strength,which is most likely related to acceleration of the pozzolanic reaction.However,the high temperature curing and dry-heat curing hinder its later strength growth,with its 28 day strength is even lower than 7 day strength.UHPC generally has lower capillary water absorption.The capillary water absorption coefficient drops remarkably with the extension of specimen suction time and curing age.The capillary water absorption of dry heat curing specimen is higher than those of other curing condition.Considering the comprehensive performance,the dry heat curing temperature should be controlled below 100℃.When the hot curing temperature is over 150℃,total and large pore porosity of UHPC will increase significantly,and the capillary water absorption will also increase.It was observed by scanning electron microscope that a few micro cracks appearal in the heat curing specimen,but steel fiber could restrain the micro cracks around the hydration products.