Reinforced Concrete Test 1 Flashcards questions and answers

Reinforced Concrete Test 1 Flashcards questions and answers Define formwork as it relates to concrete. Formwork are the molds used to give shape to and support the fresh concrete as it cures. Approximately what percentage of the total cost of cast-in-place concrete construction is associated with formwork? Formwork typically makes up 50%-55% of the total cost of a CIP structure but can be as much as 75% of the total cost for complex shapes and forms. What is shoring in concrete construction? adjustable temporary supports for formwork. What is meant by reshoring as it relates to cast-in-place concrete? The reinstallation of shoring after form removal is called reshoring. Define development length as it relates to reinforced concrete. Development length is the length a rebar must be embedded in concrete so that when tensioned the bar will yield before it slips or pulls out of the concrete. List three reasons that ties or a spiral must be included in a column. 1.Prevent the vertical (longitudinal) bars from buckling should the cover concrete spall. 2.Provide horizontal shear resistance to the column 3.Confine the concrete inside the vertical bars (core concrete) to produce a more ductile failure. What does it mean to consolidate concrete? Consolidation is the process of compacting concrete to ensure it has no voids or air pockets and completely surrounds the reinforcement. How is consolidation achieved? Consolidation is generally achieved by vibrating the concrete inside the forms (internal vibration) and/or vibrating the formwork (external vibration). For small jobs consolidation can be done by hand with a rod. Explain why flat plate, flat slab, and wide-module joists floor systems are more common than flooring systems framed with beams and girders in cast-in-place concrete construction. because they easily make use of modular formwork and can all be achieved by initially forming a flat deck. This can lead to substantial savings in formwork costs List the basic ingredients required to make concrete. Cement, Water, Fine and Coarse Aggregate. List three advantages of reinforced concrete 1.High resistance to effects of fire, water, and industrial chemicals 2.Offer architectural flexibility 3.Low maintenance cost and long service life List three disadvantages of reinforced concrete 1.Significant cost of formwork, shoring, and falsework to support fresh concrete 2.Concrete structures tend to be heavy 3.Low tensile strength requiring the use of reinforcement Explain briefly why curing of concrete should not be described as drying. When concrete cures, the mix water does not leave the mix. Portland cement reacts with water in a process called hydration to form a hardened cement paste. Thus curing is not drying, because the majority of the water remains in the concrete. What happens to concrete when it does dry? When concrete does dry (when free water evaporates) it shrinks. Some shrinkage in the concrete is unavoidable and managing the shrinkage is an important task What limits does ACI 318 place on the maximum size of coarse aggregate and why? -1/5 the minimum dimensions between the forms -1/3 the depth of slabs -3/4 the clear spacing between the reinforcement This is done to avoid honeycombing and to enable proper consolidation. Briefly explain how an air-entraining admixture improves the durability of concrete Air-entraining forms a network of tiny air bubbles in concrete that give free water a place to expand as it freezes without putting internal pressure on the concrete. Thus, air-entraining concrete improves the freeze-thaw durability of concrete. Briefly explain what a pozzolan is Pozzolans are siliceous compounds that alone do not form cementitious compounds when mixed with water, but will in the presence of water react with calcium hydroxide (a by-product of the cement-water reaction) to form a cementitious compound. Why is slag cement is not a pozzolan. Slag cement is a true hydraulic cement meaning it reacts with water to form a cementitious compound. Thus it is not a pozzolan. At what age is the compressive strength of concrete usually specified?