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Design and Control

GC Exam-Design and Control of Concrete Mixtures

QuestionAnswer
What is the binding reaction between portland concrte cement and water called? Hydration
How is the strength of concrete expressed? The strength of concrete is expressed as the maximum resistance of a concrete specimen to to axial loading. It usually megapascals (MPa) or PSI at 28 days
What is the most effective method of controlling unsightly cracking of concrete surfaces? Control Joints
Can concrete structures be used in applications that expose it saltwater? Yes, it has been used in seawater applications for decades with excellent performance
When can Type III cement be expected to reach a useable strength? Usually in one week or less
Traditionally how much does 1 U.S. bag of concrete weigh? 92.6lbs
What is the expected yield of a U.S. bag of concrete at 92.6lbs? One cubic foot
If admixtures are not present to retard the rate of setting of concrete what other methods are pratical? Reducing the temperature of the concrete by cooling the mixing water and/or aggregates
What is the maximum amount of calcium chloride that may be added to cement mixtures? In no case shall calcium chloride exceed 2% of the total mass of the mixture
Of internal or internal vibrators which is more desirable for removing air content from concrete? Internal vibrators reduce air content that external vibrators
What are the slump recommendations for various types concrete construction? Design and Control of Concrete Mixtures: Table page 115
Under normal circumstances can water be added to concrete drums before solid materials are added? Yes, normally about 10% of the water is added before the solid materials are added
What is the minimum number of revolutions of a concrete drum when remixing concrete? Minimum 30 revolutions
What is the process of cutting off the top surface of a slab to bring it to proper grade? Screeding (Strikeoff)
What are the principal causes of Crazing, dusting and scaling? Working bleed water into the surface of concrete while finishing. Finishing concrete while bleed water is present.
Will finishing concrete while bleed water is present reduce the strength of the concrete at the surface? Yes
What is one practice of finishing concrete that is intended to improve friction and decrease hydroplaning on highway concrete paving? Tining
How deep are contraction joints cut into concrete? ¼” of the thickness of the slab or a minimum of 1” deep
What is the appropriate spacing of contraction joints in concrete? Design and Control of Concrete Mixtures: Table page 208
How soon can the side forms be removed from reasonably thick sections of concrete? After 24 hours
How should shallow patched be repaired? They should be filled with a dry-pack mortar in layers not more than ½” thick with each subsequent layer being given a scratch coat to improve bonding
What are common methods used for curing concrete? Fabric coverings saturated with water such as burlap, cotton mats, rugs or other moisture retain fabrics are commly used to keep concrete surfaces wet to prevent moisture loss during curing
What is one way to prevent moisture loss when placing slab on ground? Moisten the ground the night before so that no standing water or puddles are present at the time of placement
A network pattern of fine cracks that do not penetrate much below the surface of concrete caused by minor shrinkage is called: Crazing
ACI 318 and ASTM C 93 call for concrete testing at what intervals? Not less than once a day Every 150 CY of concrete placed Every 5000 SF of surface area
A seven day compressive strength test for concrete is expected to yield what results? 60% to 70% of the anticipated 28 day strength
ASTM C172 (AASHTO T141) require concrete samples to be? At least 1 CF and obtained within the first 15 min and between the first and final portions of the sample
Created by: KKnots
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