Chapter 7, Problem 7.28QP

Students in the materials class prepared three 4″ × 8″ concrete cylinders with water–cement ratios of 0.50, 0.55, and 0.60, respectively. After curing for 7 days, the specimens were subjected to increments of compressive loads. The load versus deformation results were as shown in Table P7.28.

Assuming that the gauge length is the whole specimen height, determine the following:

1. a. The compressive stresses and strains for each specimen at each load increment.

TABLE P7.28

Specimen No.	w/c Ratio	Load (kips)	Deformation (in.)	Stress (psi)	Strain (in./in.)	Secant Modulus (psi)
1	0.50	0	0
		1	5.77E-05
		5	2.89E-04
		10	5.77E-04
		15	8.66E-04
2	0.55	0	0
		1	4.88E-05
		5	2.90E-04
		10	6.20E-04
		15	1.09E-03
3	0.60	0	0
		1	5.30E-05
		5	3.08E-04
		10	7.62E-04
		15	1.48E-03

1. b. Plot stresses versus strains for each specimen on one graph.
2. c. If the ultimate stress is 3000, 2500 and 2000 psi at 0.50, 0.55 and 0.60, respectively, determine modulus of elasticity as the secant modulus at 40% of the ultimate stress at each water-cement ratio.
3. d. Comment on the effect of increasing the water-cement ratio on the modulus of elasticity.