若干因素对新拌砂浆气泡结构及其经时变化的影响

Influence of several factors on air bubble structure and its time-dependent changes of fresh mortar

采用新拌混凝土气孔结构分析仪,考察了水灰比、灰砂比、矿物掺合料、聚羧酸减水剂等因素对新拌砂浆的含气量和气泡结构经时演变的影响规律。结果表明:总体上,新拌砂浆中存在小气泡(<300μm)数量减少、大气泡(>1 000μm)数量增多的趋势。在相同砂浆流动度条件下,增大水灰比,导致新拌砂浆含气量逐渐降低,并且大气泡占比明显增加;增大灰砂比,新拌砂浆含气量逐渐提高,同样伴随着大气泡占比的增加;粉煤灰和矿粉均能降低新拌砂浆的含气量,矿粉使得砂浆中小气泡向大气泡的转变趋缓,粉煤灰则促进气泡结构的经时转变。随着聚羧酸减水剂掺量的增加,砂浆的初始含气量和小气泡占比均明显提高,但60 min后反而伴随着更低的小气泡占比,即加剧了气泡结构经时变化的程度。

The influence of several factors on air content,air bubble size distribution and its time-dependent changes of fresh mortar,including water-cement ratio,cement-sand ratio,proportion of mineral admixture,polycarboxylate superplasticizer dosage,was investigated by using Air-Void Analyzer.The results showed that,in general the content of small air bubbles with the size below 300 μm is decreasing and the content of large air bubbles with the size over 1 000 μm is increasing over time.Under the same fluidity condition,the increase of water-cement ratio would result in a gradually decrease in air content and a slightly increase in the proportion of large air bubbles of fresh mortar.The increase of cement-sand ratio would result in an increase in air content and the proportion of large air bubbles of fresh mortar.The air content of fresh mortar was reduced with the incorporation of fly ash or slag.The incorporation of slag slowed down the transition from small bubbles to large bubbles,whereas the incorporation of fly ash accelerated the transition from small bubbles to large bubbles in the mortar.With the increase dosage of polycarboxylate superplasticizer,the air content and the proportion of small air bubbles increased significantly in the initial time.However,the proportion of small air bubbles was even lower in mortar with more dosage of polycarboxylate superplasticizer over a period of 60 minutes,which means the polycarboxylate superplasticizer lowered the stability of small air bubbles.