硬化期受扰动混凝土的抗硫酸盐侵蚀性能

凝结硬化期间的施工扰动,可能使混凝土产生砂浆微裂缝与骨料位移,进而影响其强度及耐久性。为分析硬化期扰动对混凝土抗硫酸盐侵蚀性能的影响,采用振动台模拟工程扰动,借助超声波和扫描电子显微镜(SEM)等测试手段,系统研究了硬化期受扰混凝土抗硫酸盐侵蚀的劣化规律,探讨了其损伤劣化机理。结果表明:临近初凝(贯入阻力值为3.5~11.5MPa)和临近终凝(贯入阻力值为19.5~28.0MPa)的扰动对混凝土影响较小,受侵蚀后试件质量和相对动弹模量的变化规律与未受扰混凝土基本一致。硬化中期(贯入阻力值为11.5~19.5 MPa)的扰动对混凝土性能影响明显,使混凝土抗压强度降低14%,抗折强度降低20%;硫酸盐腐蚀进程中,混凝土质量在90次循环后开始出现明显下降,相对动弹模量在130次循环后出现急剧下降,经250次循环后达到0.60,此时基准混凝土的相对动弹模量仍为0.90;SEM结果表明,受扰混凝土内部微裂纹增多,结构密实性变差,硬化期扰动加速了混凝土在硫酸盐侵蚀环境下的劣化。

Sulfate Attack Resistance of Concrete Subjected to Disturbance in Hardening Stage

The disturbance during hardening will cause mortar cracks and aggregate displacement, which can affect the later strength and durability. Using shaking table to simulate engineering disturbance, the deterioration rule of early disturbed concrete under dry wet cycle was investigated systematically by means of ultrasonic and scanning electron microscopy in order to analyze the effect of the disturbance of hardening period on the sulfate resistance of concrete. The mechanism of concrete damage deterioration was discussed. Results show that the disturbance closer to initial setting (the penetration resistance is 3.5 MPa to 11.5 MPa) and final setting (the penetration resistance is 19.5 MPa to 28.0 MPa) has smaller effect on concrete. The change rule of weight and relative dynamic elastic modulus is consistent with that of the non-disturbed concrete. The disturbance of hardening medium (the penetration resistance is 11.5 MPa to 19.5 MPa) has obvious influence on concrete. The compressive strength loss reaches above 14% and the flexural strength loss is more than 20%; in the course of corrosion, the weight of concrete decreases obviously after 90 cycles. The relative dynamic modulus decreases sharply after 130 cycle, and reaches 0.60 after the 250 cycle. The relative dynamic modulus of the concrete is still about 0.90. The results of SEM show that the internal micro cracks of the disturbed concrete increase and the structural compactness becomes worse, and the disturbance accelerates the deterioration of concrete under sulfate attack.