Research Of Cement-based Materials Under Acid Rain Corrosion Condition And Mechanism

The pollution level of environment becomes aggravated complied with the high speed development of modem industry today.The acid rain is one of the major pollution phenomenon's yielding throughout the world,which can result in the severe corrosion damage to such cementations materials as cement concrete and mortar,and lead to the heavy economic losses and consumption of resources.Therefore,it is vital for the researchers and technologists to focus on the corrosion damage caused by the acid rain for cementations materials.The paper is funded by the Hi-tech Research and Development Program of China(863 Program) No.2005AA332010 named Material & Structure Design of High Impermeability Long Service-life Large Dimension Segment of Shield tunnel and its Engineering Application.The research object is focused on issues including the corrosion damage behavior of cementations materials,mineral admixture influence factors,damage mechanism of acid rain.The principle work and conclusions are listed as follows:1.Varieties of cement,mineral admixture,such as material parameters on the material composition of the corrosion rate,have an important impact on the degree.2.The use of slag cement to a certain extent,undermines the process of slow erosion of acid rain,but still be subject to severe erosion of acid rain damage.Slag cement concrete compared to ordinary Portland concrete to reduce acid rain of corrosion in concrete under the conditions of the mass loss,its 90d and 150d mass loss are 49.6%and 69.0%to ordinary Portland concrete.Slag cement and ordinary Portland cement concrete's compressive strength and flexural strength loss (coefficient of corrosion resistance) showed the same tendency of first grown and then decreased.However,slag cement concrete's corrosion resistance ability of acid rain is stronger than the ordinary Portland concrete3.The introduction of appropriate mineral admixture to a certain extent can improve the anti-acid rain erosion performance of Portland cement.Taking the 180d Surface damage factor and Inner damage factor as the example,with 30%high calcium fly ash or 30%slag or 5%silica fume added 25%slag can decrease Surface damage factor of 9.29%and 14.84%,and Inner damage factor of 22.56%and 27.45 %.Calcium-doped low activity of fly ash cement-based materials can not improve the anti-corrosion properties of acid rain;Therefore,the improvement of different mixture of ordinary Portland cement to anti-acid rain erosion can rank ordering:30% slag>30%high calcium fly ash>30%low calcium fly ash.4.Corrosion in the acid rain conditions,the modified calcium gray mortar can significantly improve the ability of acid erosion,but there is the best to optimize its range of content,about 20%- 30%.Exceeding the "inflection point";the performance of fly ash mortar deterioration of the results will show.5.Adding of 25%modified high calcium fly ash on the mortar to anti-acid rain can strengthen the effect of corrosion loss of strength;The introduction of 25% modified high calcium fly ash mortar after 56 d of simulated acid rain corrosion, microscopic analysis in the SEM can be-observed that the high activity of high calcium fly ash particles generated by the micro-aggregate effects and volcanic ash effects,improved the pore structure of concrete,reducing porosity of concrete,so that the formation of dense concrete structure and improve the durability of concrete.6.Corrosion in simulated acid rain,the volume of the ground powder have great performance in resisting acid rain,comprehensive survey in the mass loss of mortar, compressive strength loss,loss of flexural strength and micro-changes in performance, I believe that under the conditions of this experiment when the slag content of 25% for the mortar to strengthen the role is the best.7.the corrosion destruction of cement-based materials under acid rain condition is mainly due to the coordinate erosion of H⁺ and SO₄2^-1 of the solutions:One is that because of dissolving erosion by H⁺,some binding phases such as Portlandite may form soluble salts or be decalcification to filter out;and other is that expansive erosion by SO₄^2- results in a large of expansive products.And the corrosion product consist of CaSO₄·2H₂O crystal,SiO₂·nH₂O gel and Al₂O₃·nH₂O gel and so on. Moreover,the acid rain attack procedure is a kind of surface to inner,gradual and cumulative attack procedure,which can be described by the physical model presented in the paper.8.Corrosion of the final product of acid rain mainly CaSO₄·2H₂O crystals and SiO₂·nH₂O and Al₂O₃·nH₂O,Corrosion products did not exist ettfingite.In addition, acid rain corrosion products from the H⁺ or SO₄^2- concentration,but the concentration of H⁺ and SO₄^2- and other erosion of media can affect the erosion and damage to the extent of the destruction process.9.The erosion of the acid rain continued to accumulate,resulted damaging in material,accompanied by the internal structure of the injury until completely collapse. Performance materials for the exterior surface of the initial softening of the phenomenon of plasma,then gradually rise to many micro-cracks,cracking,shedding layers,and further osteoporosis,softening and pulp,and the late emergence of the phenomenon of a large area off until completely disintegrated.