ESPECIFICACIONES TECNICAS DEL PROYECTO PARA GEOSINTETICOS

Define the frequency and types of concrete tests that are required based on type of project and purpose for the tests.

The accuracy and reliability of the quality control tests results, in representing the concrete tested, is largely dependent upon the frequency of tests performed. The frequency of your company’s quality control testing may be a function of many factors including, but not limited to:

x Project requirements;

x Evaluation of testing by others;

x Component materials analysis;

x Mix consistency and performance;

x Plant standard deviation; and

x Weather considerations According to ASTM C 94,

strength tests as well as slump, density, temperature, and air content tests shall generally be made with a frequency of not less than one test for each 150 yd³. Each test shall be made on a separate batch. On each day concrete is delivered, at least one strength test shall be made for each class of concrete.

This frequency of testing is for acceptance testing only and should not control your company’s internal quality control tests frequency.

Slump, air-content, density and temperature tests shall be made at the time of placement at the option of the inspector as often as is necessary for control checks. In addition, these tests shall be made when specified and always when strength specimens are made.

Describe your organization’s testing frequency for specific plants and/or designated concrete mixtures (for example, one test per 200 cu. yd. of plant production or one test per 50 cu. yd. for a particular designated mixture).

Preparation Guidelines for Quality Manual For Ready Mixed Concrete Companies

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consistency. This can be supported by lab tests tied to incoming shipments of materials. If you regularly sample, test, and track specific mixes, discuss your mix selection methodology, where samples are taken, who is responsible for obtaining the samples, and the information you obtain. The analysis of the data obtained will be described in Section 15, Measurement, Analysis and Improvement. 12.3 Sampling and Testing of Freshly Mixed Concrete

Outline the Company’s process and frequency for quality control tests of plastic concrete for product quality monitoring or for independent verification of acceptance testing.

Acceptance testing of ready mixed concrete requires sampling in accordance with ASTM C 172, Practice for Sampling Freshly Mixed Concrete. It is critical that sampling for acceptance testing be accomplished by the precise techniques specified in order for the sample to be representative of the concrete being tested.

For acceptance testing, samples should be taken in accordance with ASTM C 172; the sample(s) from stationary mixers and revolving drum truck mixers shall be taken during discharge from the middle portion of the batch. Samples for truck mixed concrete are generally taken at the job and samples from central mixed concrete may be taken at the plant and/or at the job site.

ASTM C 172 may not be appropriate for quality control tests conducted at the plant. If your company deviates from ASTM C 172 procedures for your internal quality control testing, it is important that you achieve consistency in your sampling process.

In some cases your company might chose to conduct independent tests to verify the results obtained by commercial testing laboratories. Establish the sampling procedure – independent sample from the same load or conduct tests on the same sample as obtained by the lab. The latter permits better comparison of testing practices. Alternatively, sample on a random basis. If detailed data are desired on concrete performance, test pre-selected loads where mixture prequalification test data exists for the mixture composition such aggregate grading; aggregate proportions; mixing water content; cement characteristics; etc.

The NRMCA Concrete Laboratory Resource Guide, illustrated as Appendix C, defines the tests on concrete that may be performed in the laboratory, the test method for each test, and the equipment that is used in conducting the test. The following standardized procedures are used for sampling and testing of the companies quality assurance purposes as identified in ASTM C 94:

x Sampling Fresh Concrete – Practice C 172

x Slump – Test Method C 143

x Density and Yield – Test Method C 138 (calculate gravimetric air content)

x Air Content – Test Method C 173 or Test Method C 231

x Temperature – Test Method C 1064

x Compression Test Specimens – Practice C 31

Discuss the decision process and responsibilities when dealing with non-conforming results either from the quality control tests or those conducted for acceptance by a testing laboratory. If the concrete slump is below the target slump range, can you add water to the concrete if a specified water/cement ratio will not be exceeded? Who is authorized to adjust the slump? Explain your company’s procedures regarding jobsite adjustments and do your procedures require a quantified limit of jobsite water

addition on a delivery ticket? Can the air content be increased on the job?

Also define your company’s process for making adjustments in the batching process to compensate for adjustments being made in the field.

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Jobsite quality control testing should be accomplished for routine mix or plant monitoring as well as for special mixes and applications. Discuss your company’s process for controlling the yield of lightweight concrete. You may perform unit weight tests on the first load and every 100 cu. yd. thereafter. It may then be necessary to adjust the batch weights for correct yield. This is sometimes very critical for structural lightweight concrete. Check tests need to be performed to determine the adequacy of yield adjustments. The testing frequency is dependent upon the variability of unit weights. A history of yield information needs to be maintained for each designated concrete mixture.

For flexural strength it is important for your company to assure compliance with the narrow slump tolerances of low slump paving concrete. Implement strict adherence to conformance testing procedures including standard methods of making, curing, and testing beam specimens. Flexural strength tests (beam test) are highly sensitive to non-standard procedures. One approach is to develop a laboratory correlation between compressive and flexural strength and recommend that the engineer of record use compressive strength tests for field samples for better reliability of the acceptance testing. For high strength concrete it is important to assure the use of concrete at a slump within the specified range; the prompt discharge of the concrete; the use of appropriate molds for test cylinders; and for strict adherence to curing and testing procedures.