Optimization of Cellular Concrete Formulation with Aluminum Waste and Mineral Additions

The paper aims to study cellular concrete with a new approach of formulation without an autoclave, with the use of aluminum waste and incorporation of mineral additions into the sand and evaluate its physical and mechanical properties. In this experimental study, two types of cellular concrete are prepared, based on crushed and dune sand with the incorporation of 15% of the slag and 10% of pozzolana, as sand replacement. An experimental program was performed to determine the compressive strength at 28 days, the density and thermal conductivity of the confected cellular concrete. The obtained results showed that concretes prepared with crushed sand developed better mechanical resistance compared to the dune sand. It is also noted that the concretes containing the mineral additions provide a substantial increase in compressive strength in particular slag. Furthermore, cellular concretes with sand dunes offer better thermal conductivity, compared to those with crushed sand. The use of the additions reduces the Water/Binder (W/B) ratio and leads to a lower thermal conductivity regardless of the used sand nature. The outcome of the present study here in could present a modest contribution for the production of cellular concrete with local materials in particular dune sand, active mineral addition and aluminum waste. The physical and mechanical properties obtained from this new composition are estimated acceptable compared to those of the industry-prepared cellular concrete product. Doi: 10.28991/cej-2021-03091721 Full Text: PDF

Evaluation of Methodologies for Assessing Self-Healing Performance of Concrete with Mineral Expansive Agents: An Interlaboratory Study

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications.

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.

Evaluation of compressive strength of concrete with metakaolin using different levelling techniques

The partial replacement of cement by mineral additions such as metakaolin has been widely applied in the production of high-strength and durable concretes due to the pozzolanic action, allowing a reduction in the consumption of cement. Tests are performed to determine the mechanical properties of these materials, such as compressive strength, for which there are different levelling techniques of specimens, such as sulphur and neoprene, indicated for different resistance classes. The present study aimed to characterize the behaviour, in the hardened state, of concrete produced with high initial strength Portland cement (CPV-ARI) and metakaolin and evaluate the different levelling methods. Three groups of samples dosed by the IPT-EPUSP method, with mix designs of 1:3, 1:5, and 1:6, and replacements of 8 and 10% of cement by metakaolin, were subjected to compressive strength test, at the ages of 28 days, with levelling by neoprene, and 90 days, with levelling by sulphur. It was observed an increase in strength with addition of metakaolin at both ages. Comparing the results in the two ages, it was verified an increase in strength for the mix designs 1:5 and 1:6 and a reduction for the mix design 1:3. Such fact can be explained by the high strengths achieved by this mix design. As the levelling method used was sulphur, it is confirmed the imprecision of results for strengths above 50 MPa with this technique.

Reduced Carbonation, Sulfate and Chloride Ingress Due to the Substitution of Cement by 10% Non-Precalcined Bentonite

The Portland cement industry is presently deemed to account for around 7.4% of the carbon dioxide emitted annually worldwide. Clinker production is being reduced worldwide in response to the need to drastically lower greenhouse gas emissions. The trend began in the nineteen seventies with the advent of mineral additions to replace clinker. Blast furnace slag and fly ash, industrial by-products that were being stockpiled in waste heaps at the time, have not commonly been included in cements. Supply of these additions is no longer guaranteed, however, due to restrained activity in the source industries for the same reasons as in clinker production. The search is consequently on for other additions that may lower pollutant gas emissions without altering cement performance. In this study, bentonite, a very common clay, was used as such an addition directly, with no need for precalcination, a still novel approach that has been scantly explored to date for reinforced structural concrete with structural applications. The results of the mechanical strength and chemical resistance (to sulfates, carbonation and chlorides) tests conducted are promising. The carbonation findings proved to be of particular interest, for that is the area where cement with mineral additions tends to be least effective. In the bentonite-bearing material analysed here, however, carbonation resistance was found to be as low as or lower than that observed in plain Portland cement.

Ocean alkalinity enhancement as a tool to mitigate ocean acidification and facilitate CO2 uptake from the atmosphere

<p>Anthropogenic global warming over the last century has led to a steady increase of CO<sub>2</sub> in the atmosphere. One of the consequences of increasing CO<sub>2</sub> concentrations is ocean acidification, a phenomenon problematic to marine biodiversity and biogeochemistry. The ocean reservoir takes up 25% of CO<sub>2</sub> from the atmosphere both chemically and biologically. This potential can be made use of to promote CO<sub>2 </sub>uptake from the atmosphere while mitigating ocean acidification and protecting biodiversity using negative emission technologies associated with the ocean. We have investigated the potential of various alkaline minerals to stabilize seawater pH overtime on a small scale. Those alkaline minerals were predicted to be appropriate for ocean alkalinity enhancement and can offer a toolset to mitigate CO<sub>2</sub> from the atmosphere. Specifically, we have examined how chalk, calcite, dolomite, limestone, and olivine affects seawater pH and total alkalinity (TA) on timescales of several months. Thereby, we could identify two promising minerals, dolomite and olivine, and develop a strategy for mineral additions to buffer the seawater pH. Importantly, the often proposed had an unexpected opposite impact and massively lowered the seawater pH over a timescale of 100 days. The identified advantageous minerals will inform our experiments on primary producer cultures and natural consortia.</p>

Chemical Shrinkage of Low Water to Cement (w/c) Ratio CEM I and CEM III Cement Pastes Incorporating Silica Fume and Filler

Chemical shrinkage (CS) is the reason behind early age cracking, a common problem for concrete with low water to cement ratios (w/c < 0.35) known as Ultra-High- and High-Performance Concrete (U-HPC). However, to avoid the crack development initiated by autogenous shrinkage, a precise measurement of CS is required, as the values obtained can determine the correct amount of internal curing agent to be added in the mixture to avoid crack formation. ASTM C1608 is the standardized method for performing CS tests. In this study, recommendations are provided to improve the reliability of results obtained with this standard method, such as good compaction of samples and the use of superplasticizer (SP) for low w/c ratios (≤0.2). Cement pastes with CEM I and CEM III have been tested at different w/c ratios equal to 0.2, 0.3 and 0.4 with and without the addition of superplasticizer. CS results following ASTM-C1608 dilatometry showed that the presence of mineral additions such as silica fume and filler reduced the chemical shrinkage, while CS increased with increasing w/c. Low w/c ratio pastes of CEM III had slightly higher CS rates than CEM I, while the opposite was noticed at higher w/c. SEM images illustrated the importance of a careful compaction and SP use.