Study of Development of Hydrating Temperatures and Reduction of Volume Changes in Concretes

One of the main characteristics in the concreting of massive waterproof structures and dam bodies is the prediction of crack formation. This prediction is associated with an understanding of the mechanics of development of hydration temperatures that affect in particular the selected binder parts of concrete. A suitable combination of cement with mineral admixtures, as well as the use of so-called shrinkage-reducing admixtures, seems to be an effective tool for influencing the dynamics of development and maximum values of hydration temperatures. Appropriate selection of the formula itself can significantly extend the lifetime of the mentioned structures. The paper is focused on monitoring the influence of different types of mineral admixtures on the effect of volume changes of cement pastes. The association of these volume changes with the development of hydration temperatures of these pastes was also observed. In order to minimize both of these phenomena, the possibility of using a shrinkage-reducing admixture was verified.

A review on the influence of shrinkage reducing admixtures on concrete

Shrinkage cracking is a common source of distress in concrete structures. In addition to being unsightly, these cracks serve to accelerate other forms of damage in concrete, thereby shortening the service life of structures. One solution to reduce the potential for shrinkage cracking is to incorporate a shrinkage reducing admixture (SRA) in concrete mixtures. SRAs belong to a special type of organic chemicals (i.e., surfactants) that when mixed in water, reduce the surface tension of the liquid, and thereby reduce the magnitude of capillary stresses and shrinkage strains that occur when concrete is losing moisture. Various studies show that SRAs have proven to reduce drying, autogenous, and plastic shrinkage, which has been summarized in this literature. Keywords—Shrinkage Reducing Admixtures, Surfactants, Drying shrinkage, Plastic shrinkage, Autogenous shrinkage.

Effects of the Sole or Combined Use of Chemical Admixtures on Properties of Self-Compacting Concrete

Chemical additives are very important in determining the behavioral characteristics of self-compacting concrete. For this reason, determining the building materials that make up the chemical structure of self-compacting concrete and the interactions of these materials is of great importance. The present study pertains to the effects of the use of different chemical admixtures (high-range water-reducing, i.e., superplasticizer, hydration accelerating, air-entraining, shrinkage reducing, and hydration heat reducing admixtures) on the fresh and hardened properties of self-compacting concrete. The influence of using a single one or a hybrid combination of the air-entraining, hydration-accelerating, heat-reducing, and shrinkage-reducing admixtures on the mechanical properties of fresh and hardened SCC was investigated through a set of tests. For this purpose, sixteen different SCC mixtures with different combinations of chemical additives were prepared and tested. The properties of fresh concrete were examined as well as the compressive and tensile strengths of the mixtures. SCC mixtures with shrinkage-reducing admixtures were evaluated in terms of shrinkage development. The effect of the use of admixtures was found to be more pronounced on the early-age concrete strength. The use of any type of additive in addition to the shrinkage reducing admixture increased the speed of flow of fresh concrete.

Effect of Shrinkage Reducing Admixture on Drying Shrinkage of Concrete with Different w/c Ratios

The reduction of the moisture content of concrete during the drying process reduces the concrete’s volume and causes it to shrink. In general, concrete shrinkage is a phenomenon that causes concrete volume to dwindle and can lead to durability problems. There are different types of this phenomenon, among them chemical shrinkage, autogenous shrinkage, drying shrinkage including free shrinkage and restrained shrinkage, and thermal contraction. Shrinkage-reducing admixtures are commercially available in different forms. The present study investigates the effect of liquid propylene glycol ether on mechanical properties and free shrinkage induced by drying at different water-cement (w/c) ratios. Furthermore, the effect of shrinkage-reducing admixtures on the properties of hardened concrete such as compressive and tensile strength, electrical resistivity, modulus of elasticity, free drying shrinkage, water absorption, and depth of water penetration was investigated. The results indicated that shrinkage reducing agents performed better in a low w/c ratio and resulted in up to 50% shrinkage reduction, which was due to the surface reduction of capillary pores. The prediction of free shrinkage due to drying was also performed using an artificial neural network.

Effect of Curing Methods on Shrinkage Development in 3D-Printed Concrete

Technological developments in construction have led to an increase in the use of 3D modelling using CAD environments. The popularity of this approach has increased in tandem with developments in industry branches which use 3D printers to print concrete based printing materials in construction, as these allow freedom in shaping the dimensions of supporting elements. One of the biggest challenges for researchers working on this highly innovative technology is that of cement material shrinkage. This article presents the findings of research on an original method of measuring deformations caused by shrinkage in 3D-printed concrete elements. It also discusses the results of tests on base mixes, as well as comparisons between the influence of internal and external curing methods on the development of deformations and their final outcomes. Furthermore, the article discusses differences between deformations formed after seven days of hardening without curing, with those which occur when two common, traditional concrete curing methods are used: foil insulation and shrinkage reducing admixtures. In addition, the article examines the effects of internal curing on the 1, 7, 14, 21 and 28 day mechanical properties of concrete, in accordance with EN 196-1 and EN 12390-2. Studies have shown that the optimal amount of shrinkage reducing admixtures is 4% (in relation to the mass of cement), resulting in a reduction in total shrinkage of 23%. The use of a shrinkage reducing admixture in 3D-printed concrete does not affect their strength after 28 days, but slows the strength development during the first 7 days.