Bond to Bar Reinforcement of PET-Modified Concrete Containing Natural or Recycled Coarse Aggregates

The use of post-consumer plastics in concrete production is an ideal alternative to dispose of such wastes while reducing the environmental impacts in terms of pollution and consumption of natural resources and energy. This paper investigates different approaches (i.e., reducing water-to-cement ratio and incorporating steel fibers or polymeric latexes) that compensate for the detrimental effect of waste plastics on the drop in concrete mechanical properties including the bond to embedded steel bars. The polyethylene terephthalate (PET) wastes used in this study were derived from plastic bottles that were shredded into small pieces and added during concrete batching at 1.5% to 4.5%, by total volume. Test results showed that the concrete properties are degraded with PET additions, given their lightweight nature and poor characteristic strength compared to aggregate particles. The threshold PET volumetric rates are 4.5% and 3% for concrete made using natural or recycled aggregates, respectively. The reduction of w/c from 0.55 to 0.46 proved efficient to refine the matrix porosity and reinstate the concrete performance. The incorporation of 0.8% steel fibers (by volume) or 15% polymers (by mixing water) were appropriate to enhance the bridging phenomena and reduce the propagation of cracks during the pullout loading of steel bars.

Use of Hemp Fibres in 3D Printed Concrete

The use of fibres as reinforcement of 3D printed concrete is widely known and applicable in many situations. However, most of the applied fibres are not produced from renewable resources. Natural fibres are commonly considered as an ecological alternative for these fibres. In order to contribute to improvement of the sustainability of 3D printed concrete, natural fibres such as hemp can replace these synthetic fibres. The objective of this study is therefore to study the possibilities of adding hemp fibres for 3D printing purposes. Due to the comparable properties of hemp and synthetic fibres, natural fibres tend to be suitable for printing purposes. Mixes are made at laboratory scale using batches of 1 – 3 kg. The study examines the effect of adding hemp fibres for the mechanical and fresh state properties of hemp-based concrete. Mechanical properties from bending tests and direct tensile tests show comparable properties of mortars containing hemp fibres and mortars containing synthetic fibres. The fresh state behaviour of the designed concrete mix showed promising and comparable results for a mix based on 0.5wt% of hemp fibres. One of the major issues regarding the use of natural fibres is the irregularity and high water uptake of the fibres. Due to its high hydrophilicity natural hemp fibres take up much water and can therefore degrade. For this study the effect of water uptake did not have much influence on the mixing and printing purposes. By printing a wall element on laboratory scale the use of hemp fibre-reinforced 3D concrete is validated.

Hybrid concretes: solutions for better bond and splitting tensile strength under elevated heat exposure

PurposeThis paper presents the second part of the investigation on resistance to elevated temperatures of a proposed hybrid composite concrete (NCSF-Crete) mix. The composite including nano metakaolin (NC) and steel fibers (SF) in addition to regular concrete components has proven -in the first published part-earlier promoted fresh concrete behavior, and to have reduced loss in compressive strength after exposure to a wide range of elevated temperatures. This presented work evaluates another two critical mechanical characteristics for the proposed composite -namely- splitting and bond strengths.Design/methodology/approachA modified formula correlating splitting and compressive strength (28 days) based on experiments results for NCSF is proposed and compared to formulas derived for regular concrete in different design codes. Finally, both spitting and bond strengths are evaluated pre- and post-exposure to elevated temperatures reaching 600 °C for two hours.FindingsThe proposed NCSF-Crete shows remarkable fire endurance, especially in promoting bond strength as after 600 °C heat exposure tests, it maintained strength equivalent to 70% of a regular concrete control mix at room temperature. Improving residual splitting strength was very significant up to 450 °C exposure.Research limitations/implicationsObvious deterioration is monitored in splitting resistance for all concretes at 600 °C.Practical implicationsThis proposed composite improved elevated heats resistance of the most significant concrete mechanical properties.Social implicationsUsing a more green and sustainable constituents in the composite.Originality/valueThe proposed composite gathers the merits of using NC and SF, each has been investigated separately as an addition to concrete mixes.

A Study on the Mechanical Characteristics of Glass and Nylon Fiber Reinforced Peach Shell Lightweight Concrete

In the current study, the utilization of glass and nylon fibers in various percentages are added to enhance the mechanical performance of peach shell lightweight concrete. Glass and nylon fibers were added at 2%, 4%, 6%, and 8% by cement weight. The results showed that, as we added the glass and nylon fibers, the density of peach shell concrete was reduced by 6.6%, and the compressive, split tensile and flexural strength were enhanced by 10.20%, 60.1%, and 63.49%. The highest strength that was obtained in compressive, split tensile, and flexural strength at 56 days was 29.4 MPa, 5.2 MPa, and 6.3 MPa, respectively, with 6% of glass fiber in peach shell concrete. Mechanical test results showed that post-failure toughness and modulus of elasticity of peach shell concrete is enhanced with the utilization of fibers. To verify our lab results, a statistical analysis, such as response surface methodology, was performed to make a statistical model, it was confirmed by both lab results and statistical analysis that the mechanical performance of peach shell concrete could be significantly improved by adding glass fibers as compared to nylon fibers. With the use of fibers, the water absorption and porosity were slightly increased. Hence, the glass and nylon fibers can be used to improve the peach shell concrete mechanical properties to make concrete eco-friendly, sustainable, and lightweight.

White Clay Ceramic Tableware Waste as Coarse Aggregate in Concrete - Some Mechanical Properties and Durability against Fire and Sulfate Attack

The aim of study is to produce durable structural concrete by using waste ceramics with specified type (white clay ceramics) as coarse aggregates in concrete. Mechanical properties were studied, the study also show good resistance to fire resistance for concrete contains ceramics as coarse aggregates compared with normal aggregates concrete, good mechanical properties such as compressive, tensile, and flexural strength. Results of study gave 17.5% increment in compressive strength by using 100% replacement of waste ceramic, flexural strength increased with 27.8% increment. Study also show less reduction in strength due to fire resistance by using waste ceramics compared to ordinary concrete, and also more durable concrete for salty water effects by using ceramic.

Calculating Dynamic Strengths of Concrete Subjected to Impact Load

The objective of this paper is to calculate the influential properties of concrete. These are the dynamic properties of sustainable concrete in the situation in which metal waste can found within its components. Growing the rate of pollution in the world, a fast decrease of the original resource, the requirement for utilization more areas of natural land, and increase the price of the newly available area are the reasons that make the researchers give great attention to the new concrete (green concrete) and destruction of unwanted material in the green mix. The concept of reuse aimed at sustainable structures was implemented within the current paper through consuming metal waste of cans and bottle caps in concrete. The waste materials were consumed in two modes; at 1st mode, it was applied in the role of fibres and mixed using 15% by weight of cement. On the 2nd mode, it was applied as coarse aggregate with 25% replaced by volume. The procedure includes testing 4 concrete mixes. The estimated properties were the flexural and compressive strengths, besides modulus of elasticity. Adding bottle caps (waste materials fibres) in concrete led to enhancement in strengths. The use of walls of cans (waste materials fibres) in concrete reduced the strengths. While in the case of compacted bottle caps plus pull-tab of cans (waste materials aggregate), concrete mechanical properties a little below the reference mix. The dynamic properties of concrete contain these types of waste under impact load were determined. As known, the dynamic properties are so helpful in the strategy that deals with civil constructions put in danger of impact loads like runways, gas explosion, etc. CEB-FIP (2010) code provides wide-ranging formulas to predict the strain change of concrete. The dynamic properties are determined by this code with consideration strain level between (10-2-100). In this range, dynamic loads in the civil constructions at the level of quasi-static strain were predicted.

A Computational Study of the Shear Behavior of Reinforced Concrete Beams Affected from Alkali–Silica Reactivity Damage

In this study, an investigation of the shear behavior of full-scale reinforced concrete (RC) beams affected from alkali–silica reactivity damage is presented. A detailed finite element model (FEM) was developed and validated with data obtained from the experiments using several metrics, including a force–deformation curve, rebar strains, and crack maps and width. The validated FEM was used in a parametric study to investigate the potential impact of alkali–silica reactivity (ASR) degradation on the shear capacity of the beam. Degradations of concrete mechanical properties were correlated with ASR expansion using material test data and implemented in the FEM for different expansions. The finite element (FE) analysis provided a better understanding of the failure mechanism of ASR-affected RC beam and degradation in the capacity as a function of the ASR expansion. The parametric study using the FEM showed 6%, 19%, and 25% reduction in the shear capacity of the beam, respectively, affected from 0.2%, 0.4%, and 0.6% of ASR-induced expansion.

Experimental Evaluation of Cement Mortars with End-of-Life Tyres Exposed to Different Surface Treatments

An end-of-Life Tyre (ELT) is a type of waste that can generate negative social and environmental impacts due to its disposal. Considering that rubber can improve concrete properties and the massive use of concrete as construction material, the addition of ELT rubber in concrete mixes is attractive. However, concrete mechanical properties are negatively affected due to the rubber-cementitious matrix interaction. Although rubber treatments have been developed to minimise the negative effects, the geo-dependency of the mix makes necessary to find cost-effective and practical solutions that will allow a real use of the ELT waste. Therefore, the objective of the present study is to characterise the properties of cement mortars with the addition of ELT rubber under three surface treatments: hydration, oxidation-sulphonation, and hydrogen peroxide. The results show that hydration is the most favourable treatment from a technical, practical, and economical point of view. In fact, with this treatment, it is possible to add up to 5% ELT rubber, with respect to the aggregate weight, and still exceed the design strength without adding more cement or additives as other investigations. The use of Portland Pozzolana Cement, with local fly ash waste, contributes as well to the promissory results obtained.

Comparative Study of High-Performance Concrete Characteristics and Loading Test of Pretensioned Experimental Beams

High-performance concrete (HPC) is subjected to wide attention in current research. Many research tasks are focused on laboratory testing of concrete mechanical properties with specific raw materials, where a mixture is prepared in a relatively small amount in ideal conditions. The wider utilization of HPC is connected, among other things, with its utilization in the construction industry. The paper presents two variants of HPC which were developed by modification of ordinary concrete used by a precast company for pretensioned bridge beams. The presented variants were produced in industrial conditions using common raw materials. Testing and comparison of basic mechanical properties are complemented with specialized tests of the resistance to chloride penetration. Tentative expenses for normal strength concrete (NSC) and HPC are compared. The research program was accomplished with a loading test of model experimental pretensioned beams with a length of 7 m made of ordinarily used concrete and one variant of HPC. The aim of the loading test was to determine the load–deformation diagrams and verify the design code load capacity calculation method. Overall, the article summarizes the possible benefits of using HPC compared to conventional concrete.