Mixture Optimization of Concrete Paving Blocks Containing Waste Silt

Most of the waste materials recycled for the production of new construction materials are by-products of various manufacturing processes, such as the aggregate washing process. Recycling such materials is of paramount importance since it could reduce the adverse environmental impacts resulting from landfilling. Various studies have attempted to recycle different types of waste materials and by-products into concrete paving blocks. However, the availability of literature on concrete paving blocks containing waste silt is quite scarce. Thus, the current paper focuses on mix design optimization and production of concrete paving blocks containing high amounts of waste silt resulting from the aggregate production process. Using the mixture Design of Experiments (DOE), 12 sets of concrete paving blocks with different aggregate blends were produced to optimize the mix design. Once the final mix design was achieved, the physical and mechanical properties of the concrete paving blocks were investigated following the EN 1338 standard. Shape and dimension measurements and various tests, including water absorption, tensile splitting strength, abrasion resistance, and slip/skid resistance were conducted on the experimental concrete paving samples. Overall, the produced concrete paving blocks showed promising properties for future applications in pedestrian walking paths.

Size effect at testing strength properties of concrete

Various strength characteristics of concrete are considered as fracture parameters. The compressive strength of concrete is of paramount importance when designing concrete structures, whereas tensile strength of concrete is the basic property when estimating cracking resistance of a structure and analysing fracture processes in concrete. When testing the compressive strength of concrete, the results are dependent on the shape and dimensions of used specimens. Some findings reported in the literature suggest that size effect exists also when testing such fracture properties of concrete as tensile strength. Unfortunately this problem is much less recognized and described compared to size effect in compressive test results. In this paper, the experimental investigation is presented on how the length of cylindrical specimens influences the tensile splitting strength of concrete obtained by means of the Brazilian method. Additional variable parameters were: type of aggregate (natural gravel and crushed granite) and cement-water ratio (C/W = 1.8 and C/W = 2.6). In conducted laboratory experiments a higher splitting tensile strength of concrete was noted for all specimens with nominal dimensions of 150×150 mm, compared to specimens 150×300 mm in size, regardless of type of aggregate or cement-water ratio.

Length Effect at Testing Splitting Tensile Strength of Concrete

Tensile strength of concrete is the basic property when estimating the cracking resistance of the structure and when analysing fracture processes in concrete. The most common way of testing tensile strength is the Brazilian method. It has been noticed that the shape and size of specimens influence the tensile splitting strength. The experiments were performed to investigate the impact of cylinder’s length on tensile concrete strength received in the Brazilian method. During the experiment the tensile concrete strength was tested on two different sizes cylindrical specimens: 150 mm × 150 mm and 150 mm × 300 mm. Experiments were performed in two stages, with two types of maximum aggregate size: 16 mm and 22 mm. The software “Statistica” was used to perform the broad scale statistical analysis. When comparing test results for shorter and longer specimens, the increase of tensile splitting strength tested on shorter cylinders was observed (approximately 5%). However, when performing deeper statistical analysis, it has been found that the length effect was not sensitive to the strength of the cement matrix and the type of aggregate but was influenced by the aggregate size. Further experiments are needed in order to perform a multi-parameter statistical analysis of scale effect when testing the splitting tensile strength of concrete.

Experimental Investigations on the Long Term Material Properties of Rubberized Portland Cement Concrete

The paper presents the results of a research work aimed at assessing the long-term strength and elastic properties of rubberized concrete. The parameters of the research were the rubber replacement of fine aggregates and the age of testing the specimens. Compressive and splitting tensile strength of concrete cylinders were obtained at the age of 5 years, coupled with the static and dynamic modulus of elasticity of all concrete specimens. Additionally, the material damping coefficient was assessed by means of non-destructive tests. The density of the rubberized concrete decreases with the percentage replacement of natural sand by rubber aggregates. A significant drop in the values of density after 5 years was observed for specimens made with rubberized concrete. The static and the dynamic moduli of elasticity decrease with the increase in rubber content. A similar trend is observed for the compressive and tensile splitting strength.

Carbstone Pavers: A Sustainable Solution for the Urban Environment

To reduce CO2 emissions from the building industry, one option is to replace cement in specific applications with alternative binders. The Carbstone technology is based on the reaction of calcium- and magnesium-containing minerals with CO2 to form carbonate binders. Mixes of carbon steel slag and stainless-steel slag, with tailored particle size distributions, were compacted with a vibro-press and subsequently carbonated in an autoclave to produce carbonated steel slag pavers. The carbonated materials sequester 100–150 g CO2/kg slag. Compressive and tensile splitting strength of the resulting pavers were determined, and the ratio was found to be comparable to that of concrete. The environmental performance of the Carbstone pavers, with an average tensile splitting strength of 3.6 MPa, was found to be in compliance with Belgian and Dutch leaching limit values for construction materials. In addition, leaching results for a concrete mix made with aggregates of crushed Carbstone pavers (simulating the so-called “second life” of pavers) demonstrate that the pavers can be recycled as aggregates in cement-bound products after their product lifetime.

MECHANICAL PROPERTIES OF RECYCLED COARSE AGGREGATE CONCRETE REINFORCED WITH STEEL FIBERS

This paper presents the combined influence of natural aggregates (NA) replacement with recycled concrete aggregates (RCA) and incorporating steel fiber reinforcement on the mechanical properties of normal-strength (30 MPa) concrete mixes. Hooked-end steel fibers were added in a 2% volumetric fraction to promote 100% RCA replacement. Fine aggregates were in the form of locally-abundant desert dune sand. Mechanical properties of 28-day concrete samples were assessed, including compression strength, tensile splitting strength, elastic modulus, flexural stress, and flexural toughness. For plain concrete mixes, the replacement of NA by RCA resulted in 18, 27, and 5% reductions in the respective design compression strength, elastic modulus, and tensile splitting strength. Nevertheless, the addition of steel fibers could restore the aforementioned properties by up to 90, 77, and 164%. Compared to the control mix made with NA, the flexural strength of the plain RCA-based concrete mix decreased by 33%, while the flexural toughness increased by 100%. In turn, the corresponding flexural properties of RCA concrete mix reinforced with steel fibers were 2 and 56 times those of the control made with NA. Findings provide evidence of the ability to produce concrete made with 100% RCA and reinforced with steel fibers with comparable compression properties and improved tensile and flexural performance compared to those of NA-based concrete.

Effect of Metal Lathe Waste Addition on the Mechanical and Thermal Properties of Concrete

The amount of steel chips generated by lathes and CNC machines is 1200 million tons per year, and they are difficult to recycle. The effect of adding steel chips without pre-cleaning (covered with production lubricants and cooling oils) on the properties of concrete was investigated. Steel waste was added as a replacement for fine aggregate in the amounts of 5%, 10% and 15% of the cement weight, which correspond with 1.1%, 2.2% and 3.3% mass of all ingredients and 0.33%, 0.66% and 0.99% volume of concrete mix, respectively. The slump cone, air content, pH value, density, compressive strength, tensile strength, tensile splitting strength, elastic modulus, Poisson’s ratio and thermal parameters were tested. It was observed that with the addition of lathe waste, the density decreased, but mechanical properties increased. With the addition of 5%, 10% and 15% metal chips, compressive strength increased by 13.9%, 20.8% and 36.3% respectively compared to plain concrete; flexural strength by 7.1%, 12.7% and 18.2%; and tensile splitting strength by 4.2%, 33.2% and 38.4%. Moreover, it was determined that with addition of steel chips, thermal diffusivity was reduced and specific heat capacity increased. With the addition of 15% metal chips, thermal diffusivity was 25.2% lower than in the reference sample, while specific heat was 23.0% higher. No effect was observed on thermal conductivity.

Influence of basalt micro-fibres on the abrasion resistance of concrete in hydraulic structures

In hydraulic structures, abrasion resistance can be a significant driver in concrete specification. Basalt micro-fibres represent a potentially sustainable construction product and have been shown to provide various benefits in concrete, however the implications for hydrodynamic abrasion resistance are to date unclear. This paper is the first investigation of its kind to examine the abrasion resistance of basalt fibre-reinforced (BFR) concretes using the ASTM C1138 underwater test method. Towards this, concretes incorporating fibre dosages of 0.5, 1, 1.5 and 3 kg/m3 were tested. The relationships between concrete abrasion and its fundamental mechanical properties are evaluated. For the particular concretes examined, it is found that based on the Shapiro-Wilks tests at 95% confidence, abrasion loss in BFR concretes followed a normal distribution; the use of basalt fibre in contents of up to 3 kg/m3 did not have a significant effect on abrasion resistance, compressive and tensile splitting strengths, as well as modulus of elasticity. It can be concluded that basalt micro-fibre can be used for their other attributes such as controlling bleeding, shrinkage and plastic cracking in concrete hydraulic structures without deleterious effects on abrasion resistance. The regression models proposed to predict concrete abrasion loss from its mechanical properties were found to be only significant at 48 h for compressive strength and 24 h for both tensile splitting strength and modulus of elasticity.

The Strength Characterisation of Concrete Made with Alumina Waste Filler

This study covers an in-depth investigation into the properties and practicality of the utilization of up to 40% Alumina Waste Filler (AWF) as a partial Portland Cement (PC) replacement material. AWF is a by-product from the recycling of aluminium, produced when salt slag is smelted and cleaned. Its use in concrete will lessen the landfill requirements for AWF disposal, and reduce the strain of the growing requirements and cost of PC. The results obtained from this study showed that the addition of AWF to the concrete mix caused a reduction in the compressive and tensile splitting strength values, and a less-workable concrete was achieved for every increase in the quantity of AWF added to each mix. The addition of AWF influenced the hydration reaction process and reduced the cumulative production of the heat of hydration over time, whilst the permeability of the concrete decreased.