....................................................................................................................................................... iii List of Figures ............................................................................................................................................... vi List of Tables ................................................................................................................................................ ix

Internal Curing: A 2010 State-of-the-Art Review

A modified uniaxial restrained shrinkage test was developed, characterized by complete automation and high accuracy of measurements. The system developed was such that tensile stresses remained constant throughout the cross-section, excluding any premature failure of specimen. This testing arrangement enables separation of creep strain from shrinkage by means of simultaneous testing of twin specimens, one under restrained shrinkage, and the other under free shrinkage. A variety of mechanical characteristics of the concrete (individual components of strain, shrinkage stresses, moduli of elasticity, creep coefficient and tensile strength) may be determined in one test. Results using this testing arrangement are presented for concrete cured in sealed conditions for 1 day and then exposed to drying at 30° C/40% RH.

Testing system for determining the mechanical behaviour of early age concrete under restrained and free uniaxial shrinkage

Freshly placed concrete exposed to hot, windy conditions is often prone to plastic shrinkage cracking, though other conditions can also promote this phenomenon This type of cracking is normally noticed on slabs, pavements, beams, and generally other flat concrete surfaces Many factors affect plastic shrinkage cracking, in particular the evaporation of water from the surface of freshly placed concrete Other factors also influence the likelihood of plastic shrinkage cracking such as water-cement ratio, fines content, member size, admixtures, and on-site building practices Evaporation itself is a function of climatic variables such as relative humidity, air temperature, the temperature of the evaporating surface, and very importantly the wind velocity at the surface This paper primarily explains the background to the evaporation nomograph found in ACI 305R-96, "Hot Weather Concreting" (Manual of Concrete Practice, Part 2-1996), where the graph provides a means of estimating the rate of evaporation of surface moisture from concrete The paper offers an alternative nomograph and various formulas to predict an evaporation rate of surface water (primarily bleed water) from freshly placed concrete surfaces Other factors related to evaporation and plastic shrinkage cracking are also addressed

Plastic shrinkage cracking and evaporation formulas

Influence of coal bottom ash as fine aggregate on fresh properties of concrete

Influence of shrinkage-reducing admixtures on the reduction of plastic shrinkage cracking in concrete

PLASTIC SHRINKAGE CRACKING OF MORTARS EXPOSED TO DIFFERENT CONDITIONS, AS PREVALENT IN HOT-DRY CLIMATES, WAS INVESTIGATED UNDER CONTROLLED CONDITIONS. THE VARIABLES STUDIED WERE AIR TEMPERATURE AND HUMIDITY, WIND VELOCITY, MORTAR TEMPERATURE, TYPE AND CONTENT OF CEMENT, AND CONSISTENCY. SHRINKAGE, TENSILE STRENGTH AND TENSILE STRESS OF FRESH MORTARS, EVAPORATION AND TIME OF CRACKING WERE MEASURED. WIDTH, DEPTH, AND LENGTH MEASUREMENTS OF THE CRACKS WERE ALSO TAKEN. THE RESULTS CONFIRM THAT RAPID EVAPORATION HAS A PREDOMINANT EFFECT ON PLASTIC SHRINKAGE CRACKING. OTHER CONCLUSIONS ARE THAT PLASTIC SHRINKAGE CRACKING IS NOT A DIRECT FUNCTION OF WATER LOSS, EVAPORATION RATE OR SHRINKAGE, AND THAT SEMIPLASTIC MORTAR DID NOT CRACK UNDER HIGH EVAPORATION CONDITIONS WHICH BROUGHT ABOUT SEVERE CRACKING OF PLASTIC AND WET MORTARS. IT WAS ALSO ESTABLISHED THAT THE FIRST CRACK COINCIDES WITH THE TRANSITION FROM THE INTENSIVE, PRACTICALLY UNRESTRAINED, LINEAR SHRINKAGE OF FRESH MORTAR TO THE MUCH SLOWER RATE DUE TO RESTRAINT ON STIFFENING OF THE MORTAR. /ACI/

Rahel Shalon

Papers

Plastic Shrinkage Cracking

The Effect of Elevated Temperature on Strength of Portland Cements