A slope of the secant between two points on the curve is known as secant modulus. Secant modulus is applicable when concrete specimen shows non-linearity or where initial tangent modulus not gives too much required information.
It is mostly applied when concrete is without any reinforcement because if initial tangent will be applied then it gives only behavior at the start of the curve either high initial modulus value (when concrete have more strength to bear stress) or low modulus value (when strains propagates faster).
In case when greater modulus value than in that case initial modulus will be preferable as compared to secant modulus, but in case when low modulus value than secant modulus will be prefer first.
Secant modulus can be determined between two points on the curve by drawing a straight line. One starts from origin and the second point will be any other point on the curve. Second point that mostly consider is almost 85% of compressive stress of concrete. After selecting two points, by drawing a straight line between these two points gives the secant modulus of particular concrete specimen.
Benefits of Secant Modulus
As secant modulus cuts the curve at two different points, so it gives better results than as compared to initial tangent modulus. Initial tangent modulus only gives value up to the point where tangent line is being touches the curve, but secant gives value between two points.