Feasibility of Using Biochar as an Eco-Friendly Microfiller in Polymer Concretes.

The circular economy includes, among other things, the use of waste materials. One such material is biochar, which should not be used as a fuel because its combustion generates large amounts of air pollution. This study evaluates the feasibility of using biochar as a partial filler in a polymer concrete. The components of the polymer concretes used in this study were vinyl-ester resin, traditional microfiller-quartz powder, waste microfiller-biochar and quartz aggregate with grain sizes up to 2 mm. The quartz aggregate was dosed at a constant rate of 1458 kg/m3 of concrete, whereas the dosage of resin and microfiller was formulated according to the experimental plan for mixtures and executed based on the volume of the remaining space: resin (65-85%), quartz powder (5-35%) and biochar (0-10%). The effects on the setting process, the consistency of the fresh composite mix and the flexural and compressive strengths were investigated. The study revealed significant deterioration of technological parameters (over 15% of biochar content makes a mixture unworkable) and slight deterioration of mechanical ones (flexural strength did not change significantly, and the compressive strength decreased by up to 15%). These results indicate that, despite some limitations, the use of biochar as an alternative pro-ecological filler is possible.

Transition Zone Enhancement with Waste Limestone Powder as a Reason for Concrete Compressive Strength Increase.

Modification of concrete with waste materials is an increasingly common process, and they are primarily used as a partial substitution for cement. In the case of inert or nearly inert additions according to EN 206, the effectiveness of such a modification mainly concerns ecological aspects and, only to a small extent, mechanical properties. This article analyses the effect of modifying cement concrete with waste limestone powder as a partial substitution for fine aggregate. The analysed waste arises as a result of the accumulation of dust produced during the initial preparation of aggregate for the production of hot mix asphalt (HMA). In order to analyse the effect of waste on compressive strength, an experimental design was prepared with variable substitution levels and variable water/cement ratios. Compressive strength tests were performed after 28 to 90 days. Statistical analysis of the results was performed. Microscopic evaluation of the fractures of the samples was carried out to clarify the mechanism of transition zone enhancement, which resulted in an increase of compressive strength of the composite.

Estimation of Post-Cracking Dissipation Capabilities of Fiber Reinforced Concretes in Three Point Bending Test Monitored with Application of Digital Image Correlation System.

Concretes with dispersed reinforcement are increasingly used in structural engineering. The basic source of knowledge on their application and design are the Model-Code 2010 guidelines. These guidelines, however, apply mainly to steel rebar reinforcement and are not fully sufficient in the analysis of the load-bearing capacity of elements made of concrete with dispersed reinforcement. Therefore, scientific research in this field is carried out continuously. The main goal of our work is to provide experimental data for the calibration of constitutive models of the cracking mechanics of concrete with reinforcement in the form of steel and polypropylene fibers. This article shows the possibility of using the digital image correlation system (DIC) to achieve this goal. The method of sample preparation and the method of conducting the tests were modeled on the recommendations contained in the PN-EN 14651: 2007 standard. The tests were carried out on prismatic elements with a notch loaded in a three-point bending setup. The results of standard strength tests are presented in the form of column graphs and tables. As an extension, the results of calculations of energy dissipated in fracture process are given. Moreover, the experimentally obtained graphs of the relationship between the force, displacement and crack opening were presented, which were supplemented with the images of crack development obtained with the use of DIC. The development of the crack net is characterized not only qualitatively but also quantitatively as a function of deflection or crack mouth opening displacement. Conclusions concerning the adopted research methodology and the tested materials are presented at the end of the article.

Chloride Diffusion in Concrete Modified with Polyacrylic Superabsorbent Polymer (SAP) Hydrogel-The Influence of the Water-to-Cement Ratio and SAP-Entrained Water.

This paper examines the influence of polyacrylic superabsorbent polymers (SAP) on the properties concerning chloride diffusion in cementitious materials. The conducted study investigated the influence of SAP on chloride diffusion in concretes of the initial w/c = 0.4 (for which the changes in compressive strength due to the SAP presence were negligible). The impact on the diffusivity of concrete of several variables was analyzed: the material characteristics of SAP, additional water added to the concrete to make up for the amount of water stored in the SAP structure, and the method of SAP dosing to the mix (either in a non-saturated form or in a hydrogel form). We found that, in the case of modifying concrete with polyacrylic SAP of a median particle size in dry conditions of 330 µm and without additional water, the coefficient of chloride ion diffusion was reduced to 65% of the reference value. The negative influence (increase) of increasing w/ctot by the amount of water initially entrained by SAP on the chloride diffusivity of concrete was identified. The conducted study indicates the premise of the mechanism of the water release from SAP in cementitious composites.

The Effect of Soil Mineral Composition on the Compressive Strength of Cement Stabilized Rammed Earth.

Cemented stabilized rammed earth (CSRE) is a building material used to build load bearing walls from locally available soil. The article analyzes the influence of soil mineral composition on CSRE compressive strength. Compression tests of CSRE samples of various mineral compositions, but the same particle size distribution, water content, and cement content were conducted. Based on the compression strength results and analyzed SEM images, it was observed that even small changes in the mineral composition significantly affected the CSRE compressive strength. From the comparison of CSRE compressive strength result sets, one can draw general qualitative conclusions that montmorillonite lowered the compressive strength the most; beidellite also lowered it, but to a lesser extent. Kaolinite lightly increased the compressive strength.

Prediction of Carbonation Progress in Concrete Containing Calcareous Fly Ash Co-Binder.

According to the European Standards (EN 450-1, EN 206), it is not permissible to use calcareous fly ash as an additive to concrete. However, other standards (for example, the American and Canadian ones) allow the use of high-calcium fly ash (type C) in concrete. As a result of brown coal combustion, a large amount of this type of fly ash is produced, and considerations on their use in concrete are in progress. Research into the influence of high-calcium fly ash on concrete durability is fundamental for dealing with that issue. The aim of the present research was to develop a new model of carbonation over time, also including calcareous fly ash content in the binder. The self-terminating model of carbonation is new, and not developed by other authors. In the current research, the former simplest model (a function of w/c ratio and time) is expanded with the calcareous fly ash to cement ratio. The basis is a statistically planned experiment with a large scope of two material variables (w/c ratio and fly ash to cement ratio). The main measured property is the carbonation depth after exposure to 4% of CO2 concentration (according to CEN/TS 12390-12). The model of carbonation obtained from this experiment is an output of the paper. Also, the idea of developing similar models for concrete families as a tool for designing concrete cover thickness for reinforced elements is described in the paper.

The Durability of Concrete Modified by Waste Limestone Powder in the Chemically Aggressive Environment.

The idea of sustainable development assumes that natural resources must be treated as limited goods and that waste must be managed rationally. This idea and the constant striving to reduce production costs make the use of waste materials as substitutes for traditionally used raw materials from non-renewable sources increasingly popular. In cement concrete technology, there are many possibilities to use waste as components of mortars and concretes. The subject of this paper is a fine-grained material, obtained as a by-product during the preparation of aggregate for mineral-asphalt mixtures. The aim of the research was to test the suitability of the selected type of powder, namely limestone powder, as a component of cement composites. The paper presents an evaluation of the potential of using the limestone powder as a substitute for the fine aggregate, focusing on the impact of such a modification on aspects of durability. The sulfate degradation and chloride ion diffusion in concrete were investigated. The overall desirability function has been determined. It was demonstrated that the satisfactory value of the general desirability can be attributed to most of the investigated concretes. Positive test results support the potential of replacing part of natural fine aggregate with the tested waste limestone dust without a negative impact on the durability of concrete.

The Influence of Dosing Method and Material Characteristics of Superabsorbent Polymers (SAP) on the Effectiveness of the Concrete Internal Curing.

This paper examines the influence of dosing method and material characteristic of superabsorbent polymers (SAP) used for internal curing, on the selected concrete properties. A new method of introducing SAP into the concrete mix and its impact on the shrinkage and compressive strength of concrete was studied. It was shown that the method of dosing SAP to the concrete mix and the differences in the properties of the tested SAPs have a significant impact on the course of changes of selected properties of the tested concrete composites. In order to compare tested series with each other and with other published results on the subject, a new method of including SAP mass content in the concrete mix, as a percentage of absorbed mixing water, was presented. The effectiveness of internal curing using different types of SAP under different dosing methods was presented as a percentage difference in tested concrete properties between modified series and reference series.