Study On Internal Curing Technology Of High Performance Concrete With Natural Volcanic Ash In Dry-zone Of Africa

Mombasa-Nairobi railway is the first section of the the East African Railway Network,and is also the first international railway to be built internationally by the Chinses standard.In accordance with the relevant requirements of the Chinese railway standards,it is necessary to add mineral admixture to the concrete to improve its durability.However,the East African region generally lacks fly ash,mineral powder and other mineral admixtures,local natural scoria with abundant reserves has become a reasonable technical choice,so this paper uses local ground scoria as mineral admixture to prepare high performance concrete(HPC).Due to the high early shrinkage of HPC,the problem of shrinkage cracking can not be neglected in the dry environment such as Africa because of insufficient external curing.Based on this,the internal curing technology is a very worthy subject for the improvement of the early shrinkage cracking of HPC with natural volcanic ash.In this paper,HPC40 and HPC60 which are used frequently at the site of project were selected,and two kingds of internal curing materials,such as volcanic slag and super absorbent polymer(SAP)were adopted.The effects of internal curing on the working performance,mechanical properties,shrinkage performance and durability of HPC with natural volcanic ash were studied.Combined with chemical binding water,internal relative humidity of concrete,water loss rate,the influence mechanism of internal curing by using SAP on the properties of concrete was analyzed.Main work and conclusions are as follows:(1)With slump and slump flow as indicators of working performance,the influence of SAP content,additional water binder ratio and different mixing processes on the workability of HPC were measured.The water absorption of SAP in the HPC with natural volcanic ash and the mixing process suitable for internally cured concrete of SAP were obtained on this basis.(2)With compressive strength as an indicator of mechanical performance,the effects of two kinds of internal curing technology on the mechanical properties of HPC were measured,the fitting relationship between the compressive strength of HPC with internal curing and internal curing water binder ration was obtained.The effect of internal curing on hydration of cementitious materials was verified by the change of chemical bonding water,and the mechanism of internal curing on strength was revealed.(3)With autogenous shrinkage and drying shrinkage as indicators of shrinkage properties,the effects of two kinds of internal curing technology on the shrinkage properties of HPC were measured,the fitting relationship between the autogenous shrinkage reduction rate of HPC with internal curing and internal curing water binder ration was obtained.Combined with internal relative humidity of the concrete,the curing effect of the internal curing on the concrete in the dry environment was proved.(4)With electric flux and carbonation depth as indicators of durability,the effects of internal curing with SAP on the durability of HPC were measured.The changes of the microstructure of the scetion of paste were observed by microscope,and based on this,the mechanism of internal curing with SAP on durability of concrete was obtained.