Combined effects of water film, paste film and mortar film thicknesses on fresh properties of concrete

• Fresh properties of concrete are governed by the water, paste and mortar film thicknesses.
• Effects of these film thicknesses on flowability, cohesiveness and passing ability are studied.
• The mortar film thickness has negative effect on flow rate but critical effect on passing ability.
• A concrete mix design method based on these film thicknesses could be developed.

It is well known that the water content, paste volume and aggregate grading have great effects on the flowability, cohesiveness and passing ability of concrete, but it is not easy to explain, quantify and predict their effects. Herein, it is proposed to evaluate their effects in terms of water film thickness (WFT), paste film thickness (PFT) and mortar film thickness (MFT). A series of concrete mixes with varying water/cement ratio, paste volume and fine/total aggregate ratio were produced for flow spread, flow rate, cohesiveness and passing ability tests. Correlation of the test results to the WFT, PFT and MFT revealed that besides the WFT and PFT, the MFT has certain effects on the fresh properties of concrete. Particularly, the MFT has little effect on flow spread, negative effect on flow rate, positive effect on cohesiveness and critical effect on passing ability. Based on these findings, suitable ranges of WFT, PFT and MFT are recommended.