Autogenous shrinkage

Autogenous shrinkage is due to the volume decrease, inherent to binder hydration reactions. This volume decrease in the solid state is mainly due to water consumption by hydration, which, for low W/C, originates desiccation. So, the autogenous shrinkage depends on rate of hydration and on the... 

The autogenous shrinkage depends on the composition of cement and will decrease in the case of cement with mineral additions and this effect will increase with the rise of the share of these additions. It is obvious, because the Itydration or poz-zolanic reaction of these additions occurs more slowly and hence they will remain much longer as the anhydrous paste cotrrponerrL The similar effect is observed in... 

ABSTRACT It is very important to determine the thermal and mechanical parameters of mortar and concrete in mesoscopic simulation. In this paper, on the basis of the Mori-Tanaka formula of mesoscopic mechanics and the concrete is treated as a two-phase composite material constituted by aggregates and mortar, the inversion of coefficient of thermal expansion, autogenous shrinkage, elastic modulus and creep were studied. This paper proposed some inversion formulas regarding these four mechanical parameters of mortar in concrete. The accuracy of these formulas was verified by FEM numerical test and demonstrated by some examples. 

Until now, much research work has been done on the prediction of composite material coefficient of thermal expansion and elastic modulus by forefathers, and many prediction methods have been developed such as the sparse method (Guanhn Shen, et al. 2006), the Self-Consistent Method (Hill R.A. 1965), the Mori-Tanaka method (Mori T, Tanaka K. 1973) and so on. However, none of these formulas take into account the parameters variation with concrete age, and there is little research on the autogenous shrinkage and creep. In the mesoscopic simulation of concrete, thermal and mechanical parameters of mortar and aggregate (coefficient of thermal expansion, autogenous shrinkage, elasticity modulus, creep, strength) are important input parameters. In fact, there is abundant of test data on concrete, but much less data on mortar while it is one of the important components. Also parameter inversion is an essential method to obtain the data, but there are few studies on this so far. 

Suppose that mortar autogenous shrinkage is s t) and age t can be divided into several increment of time At = ti to, t Ati= r, - r, then mortar autogenous shrinkage... 

After all the autogenous shrinkage increments for each period are determined, concrete total autogenous shrinkage is available by accumulation calculation as follow ... 

If concrete autogenous shrinkage is given, mortar autogenous shrinkage ean also be determined by Eq. 20, which is transformed from Eq. 18. 

Table 3. Comparison between inversion result and FEM result of autogenous shrinkage (Unit 10-6).

Concrete is treated as a two-phase composite material constituted by aggregate and mortar. This paper provides the inversion formulas of several vital thermal and mechanical parameters of mortar by Mori-Tanaka theory in meso-mechanics. With these formulas, the mortar coefficient of thermal expansion, autogenous shrinkage curve, elasticity modulus curve and creep curve can be determined conveniently. However, this paper takes no consideration of the influence of interface between aggregate and mortar. Thus further studies are needed to be done to show the effect of this factor. 

The uniaxial restrained and adjusted Temperature and Stress Testing Machine (TSTM) was used evaluate the cracking sensitivity of concretes and the thermal stresses developed in adiabatic conditions (Hu, 2007 Zhang, 2002). Fresh concrete was placed in the 150 mm X 150 mm x 1500 mm frame. The temperature of the fresh concrete should be 25 2 °C. There was no moisture exchange between specimen and the ambient, thus no dry shrinkage took place and in consequence, the deformation of specimen consisted of only autogenous shrinkage under full restraint and thermal deformation at the same time. 

Figure 2. Autogenous shrinkage of binary and ternary mixes containing FA and GGBS.

A comprehensive evaluation system was introduced to determine the early cracking tendency of box girder HPCs with inclusion of SCMs by tracking the development of thermal, physical and deformation properties, which included hydration heat test, adiabatic temperature rise test, autogenous shrinkage test and plastic shrinkage test as well as Temperature and Stress Machine test, et al. 

An Mingzhe, Zhu Jinquan and Qin Wdzu. Measures to restrain the autogenous shrinkage of high performance concrete. Concrete 2001 (5) 41 6. 

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