塑性混凝土的长期渗流溶蚀稳定性试验

为了评定塑性混凝土的长期渗流稳定性和使用年限,结合当地原材料的情况,采用膨润土、黏土、水泥、骨料、水和减水剂等来制备塑性混凝土,试验测定了完整或含孔洞塑性混凝土的长期渗流稳定性和使用年限。经过多次试配试验,选定配合比并制作试件,该试件在标准养护28 d后,其抗压强度为1.25 MPa。分别制备、使用2组共12个试件进行溶蚀试验或冲淋试验。溶蚀试验表明,在溶蚀试验的测试初期,渗透系数是不断变化的,尤其在试验前30~40 d是比较明显的,但均在10-7 cm/s数量级。随溶蚀时间的延长,混凝土试件中被溶蚀Ca O的数量呈线性递减关系,直至降低到自来水所含Ca O的浓度范围,而渗透系数在150~180 d时增至3.0×10-7 cm/s,且逐渐趋于稳定。经180 d的渗流溶蚀作用后,塑性混凝土会产生剪损裂缝和拉断裂缝,甚至有较大的塑性变形,导致试件顶面平均上升位移值高达38.5 mm。通过溶蚀试验计算该塑性混凝土的渗透系数和Ca O含量,然后计算塑性混凝土防渗墙使用年限为37.1~60.7 a。冲淋试验表明:水流会在含孔洞的混凝土中产生集中冲刷且局部混凝土中的Ca O被溶蚀并随水流携带走,经过测定分析,水流从孔中冲蚀出的白色沉淀物为碳酸钙,另有少量的Na+、微量黏土和膨润土颗粒,从而降低了混凝土的质量。在恒压水流作用下,水流对已含孔洞混凝土的冲刷较弱,混凝土中被溶蚀并携带走的Ca O较少,即使冲淋197 d后,其前后的质量的损失较小,相对损失不超过1%,但其强度损失较大,高达25.4%。综合研究表明:采用黏土和膨润土制备的塑性混凝土符合土石坝防渗墙防渗的特点,具有水泥用量小、强度低、高抗渗性和使用年限长的特点。

Experiment on long term seepage corrosion stability of plastic concrete

Abstract: In order to evaluate long-term seepage stability and service life of plastic concrete that are made of bentonite, clay, cement, soil aggregate, water, superplasticizer, etc., we studied incomplete or contain holes of plastic concrete's long-term seepage stability and service life. Specimens of plastic concrete were molded after many times of tests, and their compressive strength of 28 days was 1.25 MPa, and meet requirements impermeability grade was S1 which was test code for hydraulic concrete because water pressure measured was 0.2 MPa by step by step method. The preparation of plastic concrete permeability test required to a round-shaped specimen (top diameter is 175 mm, basal diameter is 185 mm, height is 150 mm). Type I was complete specimens of concrete impermeability; and Type II specimens were high in the direction parallel to the reserved five through holes with a diameter of 3.5 mm, plum-shaped layout was on the plane. It was found after long-term corrosion test plastic concrete can produce shear cracks and tensile cracks and even had lager plastic deformation after long-term seepage dissolution by pure water, which led to damage of the plastic concrete. This resulted in an increase of maximum displacement values of top surface of the specimen by 38.5 mm on average. The permeability coefficient was changed in the early (30 to 40 days) penetration test, but they were in 10-7 cm/s orders of magnitude. The permeability coefficient was increased to 3.0×10-7 cm/s and then tended to be stable during 150-180 days. Ca2+ were dissolved from the concrete and leached out after long-term seepage dissolution, the amount of Ca2+ removed from concrete specimens were linearly decreasing as dissolution time (<150 days). The concentration of Ca2+ in the specimen water seepage fell below 110 mg/L after 180 days of dissolution. Through dissolution experiment, calculating plastic concrete's coefficient of permeability and content of CaO were done based on the formula of diaphragm wall's durable years, the calculated service life was 37.1-60.7 years. Drench experiment showed that flows may create preferential erosion in holes in concrete, and Ca(OH)2 in concrete were dissolved and carried away by the flow which led to decrease in weight of plastic concrete. The flow of constant pressure through holes of concrete was relatively weak, and few Ca in concrete were dissolved and carried away. Even after drench 197 d, there was less quality loss compare with the original, the relative loss was not more than 1%. However the concrete strength loss was larger (up to 25.4%). The white precipitates in the hole were CaCO3, and some Na+, trace clay and bentonite particles after laboratory analysis. The studies showed that the features of plastic concrete made of clay and bentonite had a low-intensity, high impermeability and long service life which met the requirement of impervious wall of earth-rock fill dam. Thus, it can be used for embankment dam for seepage prevention.