Study On Preparation And Properties Of Nano-MgO Modified Cement Mortar

Since cement has the characteristics of auto-shrinkage deformation caused by hydration reaction,this deformation will cause the generation of cracks in cement-based materials,which will seriously affect the internal microstructure of the material,thereby affecting the comprehensive performance of cement-based materials.Compared with the traditional entringite and calcium oxide expanders,nano-MgO as an expansion agent is incorporated into cement-based materials to compensate for its self-shrinking deformation,which has good development prospects and development potential.In this paper,the addition of nano-MgO is the only variable and a blank control group is set up to study the effects of the performance of modified cement mortar with different doping amounts(0.5%,1.0%,1.5%,2.0%),including basic macro-performance(consistency,flow,pore rate,wet and dry density,mechanical strength)and durability(impermeability,crack resistance,anti-sulfur corrosion resistance,anti-freeze performance),The micro-structure analysis of modified cement mortar is carried out by Fourier infrared spectroscopy test(FTIR)and scanning electroscope test(SEM).The results of the study are as follows:(1)The addition of nano-MgO will increase the water demand of cement mortar,reduce the consistency and flow of modified cement mortar.The more nano-MgO is mixed,the less consistency and flow of modified cement mortar are;The addition of nano-MgO will increase the internal tightness of the cement mortar block and reduce the pores between the internal media of it,thus reducing the pore rate and the difference in wet and dry density of the cement mortar block.And when the maintenance age was 28 days and the amount of nano magnesium oxide was 1.5%,the pore rate and the difference in wet and dry density of the cement mortar block were lowest.The addition of nano-MgO will increase the mechanical strength of cement mortar block and the strengthening effect is most obvious in the early stage of maintenance.When the maintenance age was 28 days and the amount of nano-MgO was 1.5%,the mechanical strength of modified cement mortar block was the best.(2)The addition of nano-MgO will increase the impermeability of cement mortar block,and when the amount of nano-MgO was 1.5%,the impermeability performance of modified cement mortar block was the best.The addition of nano-MgO can play a significant control effect on the plastic shrinkage crack of cement mortar,reduce the cracking index of cement mortar block and improve the crack resistance of it,when the amount of nano-MgO was 1.5%,the cracking index of modified cement mortar test block was the smallest.The mixing of nano-MgO can enhance the anti-sulfate corrosion resistance and anti-freeze performance of cement mortar block.When the amount of nano-MgO was high,the anti-sulfate corrosion resistance and anti-freeze performance of cement mortar block were better.And the addition of nano-MgO made the anti-sulfate corrosion resistance and anti-freeze performance of cement mortar block had a certain increase by the increasing time of sulfate immersion and freeze-thaw cycles.(3)FTIR and SEM tests showed that after 28 days of maintenance,the cement mortar produced calcium hydroxide,calcium sulphoaluminate hydrate,calcium silicate hydrate and a small amount of calcium carbonate,and there still had some dicalcium silicate,tricalcium silicate and tricalcium aluminate.The nano-MgO which was incorporated into the cement mortar produced magnesium hydroxide by hydration.When the amount of nano-MgO was gradually increased from 0%to 1.5%,the amount of etrringite,calcium silicate hydrate,calcium carbonate and magnesium hydroxide which were produced in modified cement mortar were gradually increased.When the amount of nano-MgO continued to increase,the amount of etrringite decreased,the amount of calcium silicate hydrate did not change significantly.But the amount of the calcium carbonate and the magnesium hydroxide in the pores were increased,which reducing the gap between the interfaces so that the internal slurry structure of modified cement mortar were more dense.