Questions and Answers
Scales for weighing aggregates and cement shall be accurate within ____ %
The contractor shall submit in writing a job-mix formula for the mixture supported by laboratory test data within ____.
Batches may be rejected unless cement is mixed within _____ hours of contact with aggregate.
The concrete samples should be stored in a moist conditioned temperature within the range of ____ until the time of test.
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The mixing time shall not be less than _____ nor more than ____.
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The flow of water shall be uniform, and all water should be in the drum by the end of the first ____ seconds of the mixing period.
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Concrete not placed within ____ minutes from the time the ingredients were charged into the mixing drum shall be used.
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When concrete is delivered in truck mixers, additional water may be added if permitted by the Engineer within ____ minutes after the initial mixing operation.
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A sample from a bituminous mix weighs 1000 grams. If the dry aggregate weighs 950 grams, what is the % of asphalt by weight of the mix?
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The minimum penetration of the preservative with the surface of the timber piles shall be ____.
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Vibration shall operate at a frequency of ____ impulses per minute under load.
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In which DPWH item is emulsified asphalt not suitable?
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Study Notes
Weighing and Mixing of Materials
- Scales for weighing aggregates and cement must remain accurate within a specified percentage, possibly up to 2.0%.
- Frequent inspection and sealing of scales is necessary to maintain accuracy as determined by the Engineer.
- Job-mix formula for concrete mixtures must be submitted in writing to the engineer and include laboratory test data and component samples with a notice period of at least two weeks.
Concrete Mixing Regulations
- Cement must not contact aggregates unless mixed within 2.0 to 2.5 hours from the time of contact.
- Fresh concrete samples should be stored in a moist conditioned environment, maintaining temperatures between 18°C to 24°C until the time of testing.
- Mixing time for concrete should not be less than 60 seconds and no more than 120 seconds, barring exceptional mixer performance.
Water and Concrete Handling
- Uniform flow of water is critical; all water must be added to the mixer within 30 seconds of the mixing period.
- Concrete must be placed within 90 minutes from when the ingredients are charged into the mixing drum.
- When delivered in truck mixers, adding excess water to achieve the desired slump is allowed if completed within 30 minutes after initial mixing.
Testing and Quality Control
- The mass percentage wear of soil aggregate in cement/lime mixtures should not exceed 40%.
- CBR (California Bearing Ratio) machine's movable head must travel at a consistent rate of 0.05 in/min.
- Cast-in-place concrete should not be post-tensioned until the specified compressive strength is achieved, typically at least 7 days.
Penetration and Quality Tests
- Penetration tests assess asphalt's consistency within 15 minutes after mixing.
- Quality tests for asphalt are mandated at a frequency of one test for every 20 tons of material.
- The weighted percentage of asphalt in a bituminous mix that weighs 1000 grams and contains 950 grams of dry aggregate calculates to be 5.0% asphalt.
Bituminous Mix Design
- The Marshall Stability method is the most commonly utilized approach in designing and evaluating bituminous concrete mixes.
- The minimum penetration depth of preservatives for timber piles is stipulated at 100 mm.
- Emulsified asphalt is not suitable in DPWH Item 304 applications.
Vibration Specifications
- Vibration equipment should operate at a frequency range of 8,300 to 9,600 impulses per minute during load applications.
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Description
Test your knowledge on the specifications and standards required for construction materials. This quiz covers various aspects such as scales for weighing aggregates and cement, job-mix formulas, and necessary laboratory testing. Ideal for engineering students or professionals in the construction industry.
