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ce materials lab 2 - Laboratory 2 Concrete Testing Civil...

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Laboratory 2: Concrete Testing Civil Engineering Materials CRN: 40701 Date Performed: 10/22/2010 Date Submitted: 11/01/2010 Lab Group 6 Andrew Melici, Lorin Nickle, Michael Plescia, Samantha Valentine
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Introduction: The objectives of this lab are: Design and produce a concrete mixture based on the following conditions and constraints: o Exposed to brackish water o Negligible sulfate exposure o Moderate freeze-thaw exposure o Target compressive strength: 3000 pound per square inch (psi) o Only air entrainer allowed Determine rodded unit weight and slump for concrete mixture Determine compressive strength for concrete cylinders Determine the compressive strength for a concrete beam Determine the flexural strength for a concrete beam Theoretical Information/Literature: The performance of cement concrete is directly dependent on its components. Water, aggregates, binder, air, curing time, environment, and application all impact the performance. This report highlights the process of proportioning cement concrete components and determining the strength of the resulting concrete mixture. Concrete Mix Design The proportions of cement, aggregate, and water in concrete mixes affect its properties in the plastic and solid states. The Portland Cement Association specifies three characteristics of properly proportioned concrete mixtures: 1. acceptable workability (of freshly mixed concrete) 2. durability, strength, and uniform appearance(of hardened concrete) 3. economy. In order to determine the proper design proportions for concrete mixes, the following 11 steps are required. Strength Requirements In order to compensate for the variance in concrete strength due to variations in materials and the batching and mixing of the concrete, the mix design must have an average strength greater than the specified strength. In order to determine the strength requirements for concrete mix design the specified compressive strength, the variability of the concrete, and the allowable risk of producing concrete with an unacceptable strength must be known. In order to calculate the standard deviation of the strength, batches of concrete are made and many samples are tested. The American Concrete Institute (ACI) has established that the
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allowable risk is 10%, that is, less than 10% of the samples have a compressive strength less than the specified strength. Therefore the required average strength can be calculated using Equation 1. Eq.1 where = requires average compressive strength (MPa or psi) = specified compressive strength (MPa or psi) = standard deviation (MPa or psi) However, if the standard deviation in strength of the mix is large, the ACI has an additional risk condition, calculated using Equation 2. Metric US Customary Eq.2 The larger value obtained from Equations 1 and 2 determines the required average compressive strength used to proportion the mix.
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