Effects of fines in sand and water-to-cement ratio on concrete properties

Abstract

The quality of building materials has been documented to be one of the causes of building collapse all over the world. An experimental study was conducted to determine the effect of fines (clay/silt) content in sand and water-to-cement ratio on the workability, compressive strength, tensile strength and flexural strength of concrete. A total of 270 specimens were cast and tested with varying fines content in sand of 2%, 4%, 6%, 8%, 10% and 12%; and variable water-to-cement ratio of 0.55, 0.60 and 0.70. A basic 1:2:4 concrete mix ratio was adopted for the study through trial mix. Mixing, compaction, curing and testing were performed in accordance with BS and ASTM standards. The results show that, workability of concrete decreased and increased as the percentage of fines in sand and water-to-cement ratio respectively increased. The study again revealed that compressive, tensile and flexural strength of concrete increased to 4% fines content in sand beyond which they decreased at constant water-to-cement ratio. Equations for predicting the workability (Wc = -141.905 – 235.714CS + 310.476w/c; R2=0.899), and compressive strength (fcu,28 = 45.357 – 37.143CS – 41.136w/c; R2=0.848), tensile splitting strength (fct,28 = 3.532 – 3.195CS – 2.798w/c; R2=0.836) and flexural strength of reinforced concrete (fcf,28 = 30.485 – 23.076CS – 24.507w/c; R2=0.905 ) were proposed valid for 4% fines in sand and beyond. It was concluded from the study that, fines percentage in sand and water to-cement ratio beyond 4% and 0.57 respectively affect concrete properties negatively. Concrete designers and producers are therefore advised to pay attention to the percentage of fines in sand and water-to-cement ratio on site.