Development of Concrete Incorporating Recycled Aggregates, Hydrated Lime and Natural Volcanic Pozzolan

Recycling of construction and demolition waste is a central point of discussion throughout the world. The application of recycled concrete as partial replacement of mineral aggregates in concrete mixes is one of the alternatives in the reduction of pollution and savings in carbon emissions. The combined influence of the recycled crushed concrete, lime, and natural pozzolana on the mechanical and sustainable properties of concrete materials is firstly proposed in this study. In this research, unconventional construction materials are employed to produce concrete: the recycled crushed concrete is used as coarse aggregate, while lime and natural pozzolana are used as a partial replacement for cement. Substitutions of 10%, 20%, 50% of gravel are made with recycled aggregates, and 2%, 5%, 10% of cement with lime and natural pozzolan. Tests on the fresh and hardened properties, destructive (compressive strength) and non-destructive tests (sclerometer rebound and ultrasound) of mixtures are carried out. It is shown that the use of recycled materials can provide an increase in compressive strength of up to 34% with respect to conventional concrete. Life cycle cost and sustainability assessments indicate that concrete materials incorporating recycled aggregate possess good economic and environmental impacts.

Producing Sustainable Concrete using Nano Recycled Glass

Background: Many tools and techniques have been recently adopted to develop construction materials that are less harmful and friendlier to the environment. New products can be achieved through the recycling of waste material. Thus, this study aims to use recycled glass bottles as sustainable materials. Objective: Our challenge is to use nano glass powder by the addition or replacement of the weight of the cement for producing concrete with enhanced strength. Methods: A nano recycled glass powder is prepared by crushing and storming a glass bottle to obtain a Blaine surface area of approximately 28 m2/g and conforming to the chemical requirements for natural pozzolana class N, according to ASTM C618. The outcome of using nano recycled glass for theaddition and replacement of ordinary Portland cement weight on the compressive and flexural strengths of concrete at 7, 28, and 90 days is investigated. Results: The concrete mixes with 2.5%, 5%, 7.5%, and 10% replacements of cement by nano recycled glass powder show improvements in compressive and flexural strengths of up to 12.77% and 7.66%, respectively, at 28 days. Meanwhile, mixes with the addition of 5% nano glass powder show best improvements in compressive and flexural strengths of up to 11.49% and 7.46%, respectively.

Mix design of high performance concrete with different mineral additions

Purpose The purpose of this paper is to present the modeling of statistical variation of experimental data using the design of experiments method to optimize the formulation of a high performance concrete (HPC) using materials that are locally available in Algeria. For this, two mineral additions (natural pozzolana and limestone filler [LF]) were used. Both additions are added by substitution of cement up to 25%. To better appreciate the effect of replacing a part of cement by natural pozzolana and LF and to optimize their combined effect on the characteristics of HPC, an effective analytical method is therefore needed to reach the required objective. Design/methodology/approach The experimental part of the study consisted of substituting a portion of cement by various proportions of these additions to assess their effects on the physico-mechanical characteristics of HPC. A mixture design with three factors and five levels was carried out. The JMP7 software was used to provide mathematical models for the statistical variation of measured values and to perform a statistical analysis. These models made it possible to show the contribution of the three factors and their interactions in the variation of the response. Findings The mixture design approach made it possible to visualize the influence of LF and pozzolanic filler (PF) on the physico-mechanical characteristics of HPC, the developed models present good correlation coefficients (R2 = 0.82) for all studied responses. The obtained results indicated that it is quite possible to substitute a part of cement with LF and PF in the formulation of a HPC. Thanks to the complementary effect between the two additions, the workability could be improved and the strengths drop could be avoided in the short, medium and long term. The optimization of mixture design factors based on the mathematical models was carried out to select the appropriate factors combinations; a good agreement between the experimental results and the predicted results was obtained. Originality/value The coefficient of PF in Cs28 model is closer to that of LF than in Cs7 model, thanks to the complementary effect between LF and PF at the age of 28 days. It was found that the optimal HPC14 concrete (10%LF–5%PF) provides the best compromise between the three responses. It is also worth noting that the use of these two local materials can reduce the manufacturing costs of HPC and reduce carbon dioxide emissions into the atmosphere. This can be an important economic and environmental alternative.

Chloride Diffusion in Cementitious Pastes: Comparative Study between OPC and Blended Cements Containing Natural Pozzolana and Slag

Chloride apparent diffusion coefficient (Dapp) of a porous media is an indicative of its capacity to resist chloride ingress. It is used to predict the service life of reinforced concrete structures. This paper presents experimental study to measure the effect of blended cement paste containing Sudanese Natural Pozzolana (SNP) from Bayuda Desert in the Northern State on Dapp by using Bulk Diffusion Test (Nord–Test NT–Build 443). Three mixes are investigated, each mix contains 3 specimens, the first mix is a reference mix with 100% Ordinary Portland Cement (OPC) compared with second mix having another containing 75%OPC:25%NP, third mix having 50%OPC:50%GGBS. All pastes have water binder ratio of 0.55. The Dapp of 50%OPC:50%GGBS is found to be 1.794*10-6 mm2/s which is lowest among the pastes. The Dapp for 75%OPC:25%NP is 2.80*10-6 mm2/s and the Dapp for 100%OPC is 3.145 *10-6 mm2/s which is the highest.

Undissolved Ilmenite Mud from TiO2 Production—Waste or a Valuable Addition to Portland Cement Composites?

This paper presents a method of utilising ilmenite MUD created during the production of titanium dioxide (TiO2) according to the sulphate method as an additive for Portland cement composites. After the production process, undissolved MUD was additionally rinsed with water and filtrated in the factory to make it more useful (R-MUD) for implementation and also to turn back some of the by-products of the production of TiO2. R-MUD is less hazardous waste than MUD. It has a lower concentration of sulphuric acid and some heavy metals. The rinsing process raised the concentration of SiO2, which is a valuable part of R-MUD because of its potential pozzolanic activity. This means that the R-MUD might be a reactive substitute of part of Portland cement in building composites. The article presents the results of research on the pozzolanic activity of R-MUD and other materials with proved pozzolanic activity, such as silica fume, fly ash and natural pozzolana (trass). Tests were performed using thermal analysis techniques. The tests showed that the pozzolanic activity or R-MUD after three days is at the same level as silica fume and after 28 days it is twice as high as the activity of fly ash. Beyond the 180th day of curing, R-MUD had the same level of activity as fly ash. The summary is supplemented by calorimetric tests, which confirm the high reactivity of R-MUD compared to other commonly used concrete additives, already in the initial hydration period. In summary, heat of hydration after 72 h of Portland cement with R-MUD is at the same level as the heat of hydration of Portland cement with silica fume and also pure Portland cement grout. The results confirm that the process of formation of micro-silica contained in R-MUD react with calcium hydroxide to form the C-S-H phase, which is responsible for the microstructure of cement composites.