木质素磺酸钙对硬化水泥抗压强度的影响

木质素磺酸盐(简称木盐)具有较强缓凝和引气作用,可提高混凝土工作性,但过量使用会导致混凝土抗压强度急剧下降。该文从掺量、相对分子质量、亲水基、金属阳离子和糖分5个方面研究了木质素磺酸钙(简称木钙)对硬化水泥抗压强度的影响规律。结果表明,随木钙掺量增加,硬化水泥的各龄期抗压强度均下降,掺量w(木钙)=0.5%时,硬化水泥的28 d抗压强度仅为空白浆体的63.6%。其中相对分子质量为1万~5万的木钙超滤级分对硬化水泥强度的降低作用较小。木钙中糖分质量分数由12.5%降至2.8%时,硬化水泥的7 d抗压强度比可提高16%。通过氧化将木钙分子中的羟基转化为羧基,硬化水泥的3、7、28 d抗压强度比分别提高22.1%、34.7%和13.0%;通过磺甲基化将木钙的磺化度由1.36 mmol/g提高到2.48 mmol/g,硬化水泥的3、7、28 d抗压强度比分别提高36.2%、41.2%和17.9%。

Influence of Calcium Lignosulfonate on the Compressive Strength of Hydrated Cement

Owing to the retarding and air-entraining properties,lignosulfonate can improve the workability of concrete.But these two properties also bring bad effect to concrete which makes the compressive strength drop sharply when the dosage of lignosulfonate exceeds 0.25%.The compressive strength of hydrated cement decreases with increasing calcium lignosulfonate(CLS) dosage.When w(CLS)=0.5%,the 28 days′ compressive strength of hydrated cement is just 63.6% of the reference,while this reducing effect of CLS fraction with a molecular weight of(10 000)~(50 000) gained by ultrafiltration was smaller.By reducing the sugar content of commercial CLS from 12.5% to 2.8%,the 7 days′ compressive strength ratio of hydrated cement raises 16%.On the other hand,turning the hydroxyl group of CLS into carboxyl by oxidation can raise the 3,7 and 28 days′ compressive strength ratio of hydrated cement for 22.1%,34.7% and 13.0% respectively.Furthermore,increasing the sulfonated degree of CLS from 1.36 mmol/g to 2.48 mmol/g can raise the 3,7 and 28 days′ compressive strength ratio of hydrated cement for 36.2%,41.2% and 17.9%,respectively.