Study Of The Impact Of Magnesia Expansive Agent For Properties Of Concrete

New magnesia expansive agent have the characteristics of light burning low activity,it can meet the requirements of the early expansion amount and can compensate the late contraction,the delay micro expansion characteristics is the premise to realize application in civil engineering,its can lead the development direction of concrete performance optimization.The purpose of this paper is to study magnesia expansive agent in the system of low clinker cement materials how to affect the performance of concrete.Test is divided into net cement slurry,mortar,concrete through the research of the three most expansive agent of magnesium oxide cement net part explores the different dosage of flow ability of cement net,the influence of the rheological parameter.Different part of the study of colloidal magnesium oxide expansive agent dosage,the mortar under different constraint conditions of flexural strength and compressive strength.Concrete part respectively from the new concrete workability,mechanical properties,durability,expansion properties,microscopic properties of these five aspects to choose C30 concrete with C45 concrete is studied,the main conclusions of study summarized as follows:Net expansion agent is added to the magnesium oxide cement slurry,mortar and concrete,its working performance decreases with the increase of dosage of magnesia expansive agent,with high dosage of magnesia expansive agent,water reducing agent to adjust the working performance can easily generate exudation of segregation phenomenon,therefore,reasonable content of magnesia expansive agent is studied.Net cement slurry study,magnesium oxide,the mixed expansive agent can reduce the time-variant fluidity of net cement slurry,and water slurry was on full display throughout the shear thinned,but mixed with low content of magnesium oxide expansive agent can obviously improve the plastic viscosity of slurry.Part of colloidal magnesium oxide expansive agent added to mortar can reduce strength of the mortar with the age before 7 d,the later strength of mortar with the increase of the magnesia expansive agent content is reduced after increase first,content 3% ~6%,the strength increased,,at the same time constraint maintenance conditions also can raise the strength of the mortar.Concrete mechanics performance test found: C30,C45 concrete strength with the increase of the magnesia expansive agent content increased first,then decreased,and when magnesium oxide expansive agent content is 3%,the compressive strength of concrete is highest.With mold maintenance can improve the C30 concrete with C45 concrete compressive strength,but the increase of C30 concrete strength is greater than the C45 concrete strength increase.40 degrees maintenance can significantly increase the intensity of C30 concrete,and can improve the early strength,more evident than the late strength,for C45 it plays a role of tiny promote early compressive strength of concrete,the improvement of the late strength is not obvious.Inflation rate test study found: the growth trend of concrete free expansion rate with expansive agent to present that early free expansion rate is low,medium expansion rate of growth is high and expansion rate of growth is slow,the higher dosage,the concrete free expansion rate is higher.C45 concrete free expansion rate are slightly lower than that of C30 concrete under free expansion rate,the higher the dosage,the higher the concrete strength grade,free expansion rate,the lower the relative.40 degrees high temperature curing also improve mixing magnesium oxide C45 concrete expansive agent limited expansion ratio,but the extent of increase was lower than that with limited expansion ratio of C30 concrete under the condition of growth.For concrete carbonation resistance,magnesium oxide expansive agent reduced the carbonation depth of concrete,expansive agent content of magnesium oxide in within the range of 3% to 6%,the higher the content,the lower the value of carbide,magnesia expansive agent is benefit to the improvement of the carbonation resistance of concrete.