我是做工程的听说聚羧酸高性能减水剂在混凝土中很好用,请问对不?
推荐回答(2个)
聚羧酸高性能减水剂对水泥的适应性
由于聚羧酸高性能减水剂对水泥浆溶液中的离子类型和浓度不敏感,较长的侧链不易被水泥水化物覆盖,因此能较长时间发挥其分散性,它对多种水泥适应性好于萘系等高效减水剂但这只是相对而言
试验证实,聚羧酸高性能减水剂对粉煤灰的品种选择十分敏感。使用Ⅰ级灰效果较好,当使用Ⅱ级灰或Ⅲ级灰时混凝土流动性较差。有时甚至会失去流动性。这主要是烧失量较高的Ⅱ级、Ⅲ级粉煤灰碳含量较大,碳粒子对外加剂的吸附量大,从而降低了外加剂对水泥的吸附,影响了混凝土流动性。试验也发现,在使用火山灰或火山灰水泥时,掺聚羧酸高性能减水剂减水效果较差。骨料对聚羧酸高性能减水剂使用效果的影响除骨料品种级配及用量外,主要是砂石中的含泥量。当含泥量从0.5%增大到4%时,掺聚羧酸高性能减水剂混凝土的减水率下降,甚至会完全失去流动性,保坍性能也差。增大聚羧酸高性能减水剂掺量时效果也不明显,而使用常用高效减水剂时,含泥率的影响远没有掺聚羧酸高性能减水剂严重
为进一步改善聚羧酸高性能减水剂的性能,降低使用成本,最好将聚羧酸高性能减水剂与其它外加剂复配使用试验发现当脂肪族高效减水剂中掺入少量聚羧酸高性能减水剂后,混凝土减水率增大,保坍性能提高,含气量也不高,还改善了脂肪族高效减水剂易泌水的缺陷,聚羧酸高性能减水剂与脂肪族高效减水剂的复配比例应通过实验确定。木钠减水剂与聚羧酸高性能减水剂可以相溶。我们试验的国产木钠及俄罗斯进口木钠与聚羧酸高性能减水剂复配使用后减水率增大,保坍性能较好,更可喜的是虽然木钠引气量也较大,但与聚羧酸高性能减水剂复合使用后未见含气量比单一使用聚羧酸高性能减水剂增加,形成了1+1<2的效果。复配产品保水性好于掺保水剂者,至今未见有掺用该产品混凝土出现过泌水现象。
聚羧酸高性能减水剂的特点是低掺量、高减水、高增强。因此它更适用于配制减水要求更高的中高强混凝土,大流动性混凝土。加之该产品较好的保坍性能,因此在高强大流动性商品混凝土及泵送混凝土中应用效果更好。低强度等级混凝土由于所用胶凝材料较少,聚羧酸高性能减水剂很难发挥其优势。更由于低强度等级混凝土用水量偏大,少量聚羧酸高性能减水剂不能抑制混凝土产生泌水,混凝土质量很难保证。
试验发现在C30混凝土中掺用聚羧酸高性能减水剂的技术效果甚至不如常用的萘系高效减水剂。特别是早期强度,掺聚羧酸高性能减水剂混凝土特别低,因此目前国产聚羧酸高性能减水剂很少用于C30以下混凝土中。
掺聚羧酸高性能减水剂的混凝土由于液相表面张力的降低,混凝土收缩率也远远低于掺入常用减水剂的混凝土,有时甚至低于不掺外加剂的空白混凝土。这十分有利于混凝土抗裂性能的提高。大量工程报道也证实,掺聚羧酸高性能减水剂的确能减少混凝土收缩裂缝的产生。 必须指出的是如聚羧酸高性能减水剂应用不当也会加大混凝土早期泌水沉降收缩。高强混凝土本来用水量就较少,如再大量减水,如遇气温高或风速大,混凝土会加速失水,这就会加大混凝土早期干燥收缩,调查发现,多起掺用聚羧酸高性能减水剂的混凝土早期产生裂缝都是应用不当造成的(如大量泌水,过分缓凝及过量减水)。当然未能提前进行保湿养护也是重要的影响因素。
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