减水剂掺量对混凝土早期收缩的影响及调控机制研究

Influence of superplasticiser on early shrinkage of concrete and its regulation mechanism

针对减水剂掺量对混凝土早期收缩的定量影响规律,采用非接触式早期收缩试验方法,试验研究了聚羧酸减水剂掺量对不同混凝土配合比变量条件下的影响。试验结果表明:当混凝土配合比相同时,减水剂掺量较低时对早期收缩的影响很小,但掺量超过一定阈值后,早期收缩显著增加;保持坍落度相同时,无论增大水胶比还是增加浆骨比,混凝土的早期收缩都随减水剂掺量增加而变大。因此,减水剂掺量是影响混凝土早期收缩的关键因素,在配合比设计中必须对其严格控制。当混凝土的和易性不能满足设计和施工要求时,增加胶凝材料用量和用水量可以减少对减水剂掺量的需求,从而降低早期收缩开裂风险。

It presents the influence of the superplasticizer dosage on early shrinkage at different mixing proportion of concrete by non-contact type shrinkage test.The test results showed that the early shrinkage of concrete would increase significantly if the dosage of superplasticizer exceed a certain threshold at the same mixing proportion of concrete,but not for concrete with low dosage of superplasticizer.If the slump remained unchanged,no matter water-binder ratio increased or paste-aggregate ratio reduced,the early shrinkage of the concrete would increase with the dosage of superplasticiser increasing.Hence,the dosage of superplasticiser is a key factor for the early shrinkage of concrete,which must be strictly controlled in the mix proportion design.Increasing gel material content and water consumption can reduce the need for dosage of superplasticizer when the workability of concrete cannot meet the design and construction requirements,which can reduce the risk of early shrinkage cracking.