Research On The Effect Of Carbonation And Sulfate Erosion On The Damage Of Cement Mortar

Reinforced concrete structures have been used in civil engineering for more than a hundred years.Most of the reinforced concrete structures in practical engineering are mostly under compbined action of mechanical and environmental loads.In the coastal areas of China and the West Saline Lake area, sulfate and carbonation are very common environmental loads,so it is very important to study the single function or the composite effect of it.Firstly, this paper studied the relative dynamic elastic modulus, the flexural and compressive strength, the CaCO3 content of the mortar specimens which are under carbonation; secondly, the paper studied the length change of specimens, the relative dynamic elastic modulus, the flexural and compressive strength, the sulfate ion content of the mortar specimens which are under sulfate attack; lastly, the paper studied the the flexural and compressive strength, the relative dynamic elastic modulus, the CaCO3 content of the mortar specimens which are under compound action of sulfate attack and carbonation. The mortar specimens contained two types of cement (ordinary portland cement, high sulfate resistant cement) and three water cement ratios(W/C=0.4,0.5,0.6) respectively. The main results are as follows:(1) when the cement mortar specimens are under carbonation,within the limited cement mortar specimens, the relative dynamic elastic modulus of cement mortar specimens increase with the increase of the carbonation time, but the growth rate decreases with the increase of the carbonation time.(2) when the cement mortar specimens are under carbonation, the compressive strength of cement mortar specimens increased with increasing carbonation time. While the water cement ration(W/C=0.4) is smaller, the flexural strength increases with the increase of carbonation time, while the water cement ration(W/C=0.5,0.6) is bigger, the flexural strength of cement mortar specimens increase first and then decrease with the increase of carbonation time. When the specimens are under carbonation for 28d, the maximum compressive strength of the specimens increased 40%-50%, the maximum flexural strength increased 20%-30%.(3) Ordinary portland cement mortar specimens immersed in water for 180d, the length increased 0.02%～0.04%, when the ordinary portland cement mortar specimens immersed in 5% sulfate salt solution for 180d, the length increased 0.04%～0.09%. High sulfate resistant cement mortar specimens immersed in water for 180d, the length increased 0.02%～0.04%, when the high sulfate resistant cement mortar specimens immersed in 5% sulfate salt solution for 180d, the length increased 0.03%～0.05%.(4) The flexural strength and the compressive strength of the specimens all increase with the increasing soaking time. When the specimens had been immersed in water for 180d, the flexural strength increased 20%～30%, the compressive strength increased 50%～60%; The flexural and compressive strength of the specimens increased with the increase of the time of the bubble, and then decreased:the maximum flexural strength of ordinary portland cement mortar specimens increased 20%～30%, and the maximum compressive strength was increased by 40%～50%. When the specimens had been immersed in the 5% sulfate salt solution for 180d, the flexural strength decreased 10%～30% than the maximum flexural strength and the compressive strength decreased 10%～40% than the maximum compressive strength. the maximum flexural strength of high sulfate resistant cement mortar specimens increased 20%～30%, and the maximum compressive strength was increased by 50%～60%. When the specimens had been immersed in the 5% sulfate salt solution for 180d, the flexural strength decreased 20%～30% than the maximum flexural strength and the compressive strength decreased 10%～20% than the maximum compressive strength.(5) When the specimens had been immersed in the 5% sulfate salt solution for 180d, the content of free sulfate ion increases with the depth of penetration, After 6～10mm from the surface of the mortar, the ion content of free sulfate ion was stable.(6) In the period of the age of the erosion and the age of carbonation, the flexural and compressive strength of the specimens increased first and then decreased under the compound action of sulfate attack and carbonation.(7) Sulfate attack can accelerate the carbonation reaction.