Increasing the water/cement ratio of concrete might make it _______ but also _______.

Concrete near the top of deep members tends to be stronger than the concrete lower down.

A wall footing has the following conditions. Determine the pressure that acts on the soil. Assume the footing is 4 ft wide.The bottom of the footing is at a depth of 4 ft below grade.The service dead load is 6 kips/ft, and the service live load is 6 kips/ft.The wall is 14 in. thick.The footing is 13 in. thick.The allowable soil pressure, qa, is 4,000 psf.The soil has a density of 110 lb/ft3.The concrete has a density of 150 lb/ft3.The concrete cover has a thickness of 3 in.f’c = 3,000 psi and fy = 60,000 psi.

A group of 20 tests on a given type of concrete had a mean strength of 4,800 psi and a standard deviation of 400 psi. Does this concrete satisfy the strength requirement for 4,500 psi concrete?

A wall footing has the following conditions. Determine the minimum cross-sectional area of the reinforcement. Assume the footing is 3 ft wide and the pressure that acts on the bottom of the footing is 6,133 psf.The bottom of the footing is at a depth of 2 ft below grade.The service dead load is 6 kips/ft, and the service live load is 7 kips/ft.The wall is 16 in. thick.The footing is 11 in. thick.The allowable soil pressure, qa, is 4,700 psf.The soil has a density of 115 lb/ft3.The concrete has a density of 150 lb/ft3.The concrete cover has a thickness of 3 in.f’c = 3,000 psi and fy = 60,000 psi.

Subfreezing temperatures can significantly decrease the compressive and tensile strengths and the modulus of elasticity of moist concrete.

Concrete subjected to critical stress of about _______ of its short-time strength will eventually fail under that load.

The concrete containing Type I cement in a structure is cured for 4 days at 70°F, followed by 4 days at 65°F. Use the maturity concept to estimate its strength as a percentage of the 28-day strength under standard curing. Maturity is defined as M = Σ(Ti + 50)(ti) where Ti is in degrees F and ti is in days.

The concrete containing Type I cement in a structure is cured for 2 days at 58°F, followed by 2 days at 43°F. Use the maturity concept to estimate its strength as a percentage of the 28-day strength under standard curing. Maturity is defined as M = Σ(Ti + 50)(ti) where Ti is in degrees F and ti is in days.

The standard compressive strength acceptance test is performed on concrete cylinders that are how old?