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Design and Control
GC Exam-Design and Control of Concrete Mixtures
| Question | Answer |
|---|---|
| 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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