Shrinkage Test

SHRINKAGE TEST INTRODUCTION This paper descripts the results of an experimental investigation carried out to determine the shrinkage of the high strength concrete. To compare the shrinkage strain for in order to choose the better type of concrete in control the shrinkage crack of concrete. PROBLEM IDENTIFICATION Plastic shrinkage normally occurs after the fresh concrete place during the first few days. When the water evaporates from the surface of freshly placed concrete faster than it is replaced by bleed water, the surface concrete shrinks. Paste of rich mixes such as high strength concrete will be more susceptible to plastic shrinkage than normal concrete. The drying shrinkage crack appears as the inevitable especially the under side of the desk slab. It seems common defects for a bridge after long term. It happens after the concrete had already attained its final set and a good portion of the chemical hydration process in the cement gel has been accomplished. Both shrinkages will be measure during this experiment. The dial gauge reading will be taken for the 1st 7 days and 14, 28, 56 and 90 days. The changes in length of each specimen were calculated from the different of final and initial dial gauge readings. Then shrinkage strain was calculated. ALTERNATIVE PREVENTIVES Low shrinkage aggregate The low shrinkage concretes may be produced by the low shrinkage aggregate which ever high specific gravity and low absorption. It might produced by using quart, limestone, granite , dolomite, feldspar where as the use of greywacke, sand stone, slate , hornblende and basalts may produce high- shrinkage concrete. Then because of the elasticity of certain aggregates such as limestone and dolomite can be vary over wide range. Hence the effectiveness in restraining drying shrinkage wills also varies. Somehow when an aggregate producing low shrinkage is not economically available. Use the lowest amount of mix water required for workability; do not permit overly wet consistencies. Consider using a shrinkage-reducing admixture to reduce drying shrinkage, which may reduce shrinkage cracking. Because almost all concrete is mixed with more water than is needed to hydrate the cement, much of the remaining water evaporates, causing the concrete to shrink. Consider using synthetic fibers to help control plastic shrinkage cracks. THEORY FOR PREDICTING SHRINKAGE OF CONCRETE Correction factors are applied to the ultimate value for condition other than the standard concrete composition. 1) Loading age 2) Differential shrinkage

3) 4) 5) 6)

Initial moist curing Ambient relative humidity Average thickness of member/volume –surface ratio method Temperature other than 70 F

The shrinkage can be estimated from Schoree’s formula (Concrete technology by Gambhir, M.L Publisher-Mc.GrawHill) Є s = 0.00125(0.95-h) where ∈s= Shrinkage strain, h= Relative humidity expressed as a fraction. ESTIMATION FOR DRY SHRINKAGE OF CONCRETE The principle variables that affect the shrinkage are listed at the theory of prediction of shrinkage above. The design approach refers to the “standard condition” and correction factors. The following general procedure is suggested for prediction shrinkage of concrete is: (ϵsh)t=t∝f+t∝(ϵsh)u Where f in days and α considered constant for a given member shape and size which define the time ratio part. (ϵsh)u Indicated the ultimate shrinkage strain, and t is the time from the end of the initial curing. Shrinkage after age 7 days for moist cured concrete (ϵsh)t=t35+t(ϵsh)u In the absence of the specific shrinkage data for local aggregates and conditions, the average values suggest for (ϵsh)u = 780γsh x 10-6 (m/m) Where γsh=1.40-0.0102 λ, for 40< λ