Lightweight SFRC Benefitting from a Pre-Soaking and Internal Curing Process

Abstract

The presented research program is focused on the design of a structural lightweight fiber-reinforced concrete harnessing an internal curing process. Pre-soaked waste red ceramic fine aggregate and pre-soaked artificial clay expanded coarse aggregate were utilized for the creation of the mix. Copper-coated steel fiber was added to the mix by volume in amounts of 0.0%, 0.5%, 1.0%, and 1.5%. Test specimens in forms of cubes, cylinders, and beams were tested to specify the concrete characteristics. Such properties as consistency, compressive strength, splitting tensile strength, static and dynamic modulus of elasticity, flexural characteristics, and shear strength were of special interest. The achieved concrete can be classified as LC12/13. A strength class, according to fib Model Code, was also assigned to the concretes in question. The proposed method of preparation of concrete mix using only pre-soaked aggregate (with no extra water) proved to be feasible.is the creation of a concrete mixture which contains the already-mentioned pre-soaked aggregates, limited amount of cement (about 300 kg per 1 m 3 ) and different amount of steel fiber without using additional water. Determined material characteristics of the fresh mix and hardened concrete would be influenced solely by water trapped in both porous aggregates and the process of internal curing [3]. Using only pre-soaked aggregate and no extra water would significantly simplify the production process of lightweight concrete. The novelty of the conducted research program is fully associated with this issue.The suitability of lightweight concrete for construction applications is conducted by the needed properties: density, strength, and thermal conductivity. Nevertheless, other properties, such as workability, water absorption, drying shrinkage and moisture movement should also be considered. The porous structure of lightweight aggregates causes high and rapid water absorption during preparation of the fresh mix. Thus, if dry porous aggregate is used for the creation of a mixture, it rapidly absorbs free water, and the workability of the fresh concrete mix is significantly affected [2]. Although the saturation of aggregates can initially cause the increase of the concrete density, it improves the concrete's long-term maturation by slowly releasing water from pores. The internal curing process significantly influences the speed and quality of cement hydration. It leads to the enhancement of mechanical properties of hardened concrete and reduces autogenous shrinkage [3].An important aspect of the research program is to deepen the knowledge about the usage of waste red ceramic aggregate. The recycling and usage of waste material in the construction field have been discussed by many research groups [3][4][5][6][7][8][9][10][11], but in practice, it is still not very common to reuse the old material as a part of new concrete. However, to encourage extensive further usage, there is need to establish a standardization for waste aggregate concrete.

Properties of Concrete with Recycled Concrete Aggregate Containing Metallurgical Sludge Waste

“…Therefore, it is worth considering the recovery and use of other materials as an alternative to natural aggregates-various types of industrial waste and demolition rubble from buildings such as bricks or concrete [21,22].…”

Durability Characteristics of Concrete Mixture Based on Red Ceramic Waste Aggregate

“…The requirements for the studied concrete mixture were very specific: using only pre-soaked aggregates and no additional water, specific density (to ensure the classification as a lightweight concrete), good workability of the fresh mix, and minimum voids on the surface of the sample (closed structure). These requirements were fulfilled, and the entire process of design, along with material characteristics, is described in detail in [9]. The consistency of SLWAC was measured by slump test as S2 according to [30] and the density of SLWAC after 24 h from casting was 1367 kg•m −3 ; therefore, the concrete can be classified as lightweight because the maximum density of lightweight concrete is given by [31] as 1800 kg•m −3 .…”

“…As has been already mentioned above, aggregates were pre-soaked, and no additional water was added to the mixture during the mixing process [9]. Therefore, during the harnessing, concrete benefitted from the process of internal curing, which is a phenomenon based on slowly releasing the water from the aggregate for hydration of the cement.…”

“…The static modulus of elasticity was determined by the tests procured on standard cylinders. The tests and evaluation of results are described in detail in [9,22]. Measured mechanical properties are used for the first and basic comparison of the waste aggregate concrete mixture and the reference mixture.…”

“…The aim of the article is to compare the quality characteristics, such as mechanical properties and durability parameters related to chloride diffusion of structural lightweight waste aggregate concrete (SLWAC), and compare them to a reference concrete mixture. The mechanical properties of the mixture have been presented previously in [9], and for the evaluation of the quality of concrete mixture the durability properties in selected exposure conditions are needed as well. The following durability tests were conducted, namely, resistivity tests and accelerated chloride penetration by NT Build 443.…”