Strength reduction and strength-scaling relations of M40 concrete with untreated bamboo chips as partial coarse-aggregate replacement

Abstract Bamboo is cheap and plentiful in Bangladesh. Its use as coarse aggregate has so far been tested mainly in normal-strength concrete (20–31 MPa). Here, untreated, seasoned bamboo chips replaced 0, 4, 8, 12 and 16% by volume of the crushed-stone coarse aggregate in an M40 concrete (40 MPa target strength, water–cement ratio 0.40). Slump and 28-day compressive, splitting tensile and flexural strengths were measured. Compressive strength decreased linearly by 1.79 MPa per 1% of bamboo (R2 = 0.996), from 44.2 MPa to 15.4 MPa at 16% (−65%). Flexural and splitting tensile strengths fell less, by 46% and 41%. Bamboo content had a significant effect on all three strengths in an analysis of variance (p < 10−6), but slump changed by only 3.5 mm. Flexural and splitting tensile strengths followed power laws of compressive strength with exponents of 0.56 and 0.45, both statistically consistent with the square-root relation of the American Concrete Institute building code (ACI 318). Measured flexural strengths exceeded the ACI 318 modulus of rupture by 3–13% at every replacement level. The strength losses fall between published values for oven-dried and water-soaked chips, which points to the moisture condition of the chips as the main factor that can be controlled. Replacing 4–8% of the coarse aggregate retained 66–81% of the control compressive strength (29–36 MPa), which is enough for ordinary structural grades. Above 8%, the concrete suits non-structural uses unless the chips are treated.