M. Bederina

Properties of flowable sand concretes reinforced by polypropylene fibers

This paper presents an experimental research on fresh and hardened properties of flowable sand concretes (FSC) reinforced by polypropylene fibers (PF). Tests were conducted on both plain and fiber-reinforced FSC. The fresh properties are tested for viscosity using a programmable DV-II + viscometer. For the physical and mechanical properties, drying shrinkage, flexural, and compressive strengths, as well as micro-structural analyses have been studied. Results indicate that all studied mixtures have a pseudo-plastic behavior in fresh state and can be well fitted using power law model. Results also confirmed that PF incorporation increases the viscosity and reduces free shrinkage of FSC. In terms of mechanical strength, results show that incorporating PF would enhance flexural strength. However, a reduction in compressive strength is observed.

Physico-mechanical properties of mortars based on the addition of dune sand powder and the recycled fines using the mixture design modelling approach

Abstract Physico-mechanical properties of mortars based on the addition of dune sand powder (DSP) and the recycled fines (RF) using the mixture design modelling approach were investigated. This experimental program aims to provide solutions and answers on the use of DSP and the recycled concrete waste in the form of fines for manufacture of the mortar having good properties. For this purpose, both additions are added by substitution of cement up to 25%. Through the results obtained, we have noticed the interest of modelling the response studied by a polynomial which is then able to calculate all the responses of the field of study without being obliged to make all the experiments. The obtained results showed that the introduction of DSP and RF in cement (by substitution) leads to a considerable improvement of mechanical strengths. The dosages of the three factors have optimum values (respectively around 66.66% of cement, 33.33% of DSP, 0% of RF in substituted volume of 112.5 kg of cement) for which the compressive strength (Cs) reaches a maximum value. Cs increases when the percentage of additions increases till an optimum (8.33% DSP, 8.33% RF), then decreases for larger percentages. One can observe that after 28 days, highest flexural strengths are that of mortars M7 and M9, with an optimum effect for the mortar M7. In addition, the modelling of the workability shows that the presence of DSP improves the workability of the mortars in the fresh state. Recycled fines have a negative effect on the flow time.

Combined effect of sand grain size and contents of wood and filler on the physicomechanical properties and the microstructure of lightweight sand concrete

Abstract This paper attempts to model the main physicomechanical properties of a wood sand concrete using the ‘design of experiments’ method. The limestone filler content (F), the maximum diameter of sand grain (D), and the wood content (B) were taken as independent variables; while the dry density (d), the thermal conductivity (C), and the compressive strength (Rc) were taken as responses. For this study, experimental tests were performed and the above method was applied. The obtained results showed that the most significant variable that affects all the studied responses is ‘B.’ The effect of the other factors is relatively weaker with very clear domination of the factor ‘D’ compared to the factor ‘F’ which seems to be very negligible. Although it is also lower than those of ‘B’ and ‘D,’ the effect of the binary and ternary interactions (D×B, F×B, F×D and F×D×B) seems to be slightly higher than that of (F). In addition, the SEM analysis highlighted the more or less homogeneous aspect of the studied composite as well as the good adherence ‘wood-matrix’ and confirmed the dominant effect of the factor ‘B’ on the microstructure evolution of sand concrete. Moreover, according to ‘B’ it is possible to develop both structural concretes and structural-insulating concretes.

Effect of ternary binder on the mechanical and microstructural properties of sand concrete

Abstract The present work focuses on the study of effect of the cement content (C), lime (L) and pozzolan (P) as well as the effect of their combinations C*L, C*P and L*P on the mechanical and microstructural properties of sand concrete based on a ternary binder using the ‘mixture design’ method. C, L and P were taken as independent variables, while the flexural strengths (Rf) and the compressive strengths (Rc) at 7 and 28 days were taken as responses. Mathematical models were determined. The obtained results showed that the most significant variable that affects all the studied responses is the cement content. The SC09 (100% C) presented the highest values. However, the SC08 (80% C + 20% L) ranks second and the SC13 (80% C + 20% P) ranks third in terms of mechanical strength. But SC08 and SC13 provided 20% of cement economy, while the minimum values of mechanical strength were recorded in the case of SC17 (100% L), which means that a high rate of lime has relatively a negative influence on the mechanical strength. On the other hand, the X-ray diffraction study showed that the type of the resulting hydration products and their quantities depend on the proportions of C, L and P, which justifies the changes recorded in the properties studied. Finally, the microscope visualization showed also that the material appears relatively homogeneous and dense with a good adhesion paste-aggregate, either in the case of cement or pozzolan or lime.

Study of the influence of the interfacial transition zone on the elastic modulus of concrete using a triphasic model

Abstract Concrete can be considered as a three-phase composite material composed of cement matrix, aggregate particles, and interface transition zone (ITZ). Generally, the ITZ presents particular characteristics that can reduce the properties of concrete and therefore limits its performance. Thus, with such complex structures, this zone is the weakest zone of the composite. The evaluation of the effective behavior of composite using predictive models requires a consideration of this zone. In this context, an approach based on the model of double inclusion and on the Mori–Tanaka theory to predict the elastic modulus of concrete has been used. This approach will be compared with some analytical biphasic model such as Reuss model, Voigt model, the Voigt and Reus combined models, and Hashin and Shtrikman models. Many experimental results are considered in the confrontation. So the developed model predicts very satisfactorily the elastic modulus of the concrete unlike other models in which a discrepancy in the results is demonstrated in the majority of cases.