AASHTO T 276-17 pdf free download

AASHTO T 276-17 pdf free download.MeasuringI Early-Age Compression Strength and Projecting  Later-Age Strength.
5. SIGNIFICANCE AND USE
5.1. This test method provides a procedure to estimate the potential strength of a particular test specimen based on its measured strength at an age as early as 24 h. The early-age test results provide information on the variability of the concrete production process for use in process control.
5.2. The relationship between early-age strength of a test specimen and strength achieved at some later age under standard curing depends upon the materials comprising the concrete. In this test method, it is assumed that there is a linear relationship between strength and the logarithm of the maturity index. Experience has shown that this is an acceptable approximation for test ages between 24 h and 28 days under standard curing conditions. The user of this method shall verify that the test data used to develop the prediction equation are represented correctly by the linear relationship. If the underlying relationship between strength and the logarithm of the maturity index cannot be approximated by a straight line, the principle of this test method is applicable provided an approximate equation is used to represent the nonlinear relationship.
5.3. Strength projections arc limited to concretes using the same materials and proportions as the concrete used to establish the prediction equation.
Note I —Confidence intervals developed in accordance with the appendix are helpful in evaluating predictions.
5.4. This test method is not intended for estimating the in-place strength of concrete. ASTM (‘1074 provides procedures for using the measured in-place maturity index to estimate in-place strength.
6. APPARATUS
6.1. Equipment and Small Tools—For fabricating specimens and measuring the characteristics of fresh concrete; shall conform to the applicable requirements of R 39 or T 23.
6.2. Molds—Shall conform to the requirements for cylinder molds in M 205M/M 205.
6.3. Temperature Recorder:
6.3.1. A device is required to monitor and record the temperature of a test specimen as a function of time. Acceptable devices include thermocouples or thermistors connected to a continuous chart recorder or digital data-loggers. For digital instruments, the recording time interval shall be I2 h or less for the first 48 h and I h or less thereafter. The temperature recording device shall be accurate to within ±1°C (±2°F).
6.3.2. Alternative devices include commercial maturity instruments that automatically compute and display the temperature—time factor or the equivalent age as described in ASTM C 1074. Note 2—Commercial maturity instruments use specific values of the datum temperature to evaluate the temperature—time factor or of the Q-value to evaluate equivalent age. Refer to the appendix of ASTM C 1074 for additional explanation and recommendations.
7. SAMPLING
7.1. Sample and measure the properties of the fresh concrete in accordance with R 39, R 60, or T 23.
8. PROCEDURE FOR EARLY-AGE AND PROJECTED STRENGTHS
Mold and cure the specimens in accordance with R 39 or T 23, whichever is applicable. Record the time when molding of the specimens is completed.
8.2. Embed a temperature sensor into the center of one of the specimens of the sampled concrete. Activate the temperature recording device. Continue curing for at least 24 h. Maintain a record of the concrete temperature during the entire curing period.
8.3. capping and Testing—For specimens cured in accordance with T 23 or R 39, remove the specimens from the molds as soon as practicable after 24 h. For specimens subjected to accelerated curing, remove molds at elapsed times prescribed in ASTM C1768/C1768M. Cap the specimen in accordance with T 231 or ASTM C1231/C1231M.AASHTO T 276-17  pdf download.