El-Hadj Kadri

Some Engineering Properties of Concrete Containing Natural Pozzolana and Silica Fume

Abstract Ternary blended cements are often used in cement manufacture using industrial waste and natural resources to produce a low cost and an environment friendly cement. Ternary blended cements also have the advantage of combining the synergic effects of their ingredients, which compensate for their mutual weaknesses. In this paper, the effect of combining a very active mineral addition (silica fume) SF on the mechanical properties and durability of cements containing natural pozzolana NP is analyzed. The optimal couples ″natural pozzolana/silica fume″ proposal is based on their mechanical properties and durability performance. The results confirm that the use of ternary cements contributes to the improvement of strength at an early stage. Better resistance to sulphate and acid attacks and less chloride ions penetration also enhanced durability.

Effects of experimental ternary cements on fresh and hardened properties of self-compacting concretes

Abstract Self-compacting concrete (SCC) is a concrete that flows alone under its dead weight and consolidates itself without any additional compaction and without segregation. As an integral part of a SCC, self-compacting mortars (SCMs) may serve as a basis for the mix design of concrete since the measurement of the rheological and viscosity properties of SCC is often impractical due to the need for complex equipment. This paper discusses the properties of SCM and SCC with mineral additions. ordinary Portland cement (OPC), natural pozzolana (PZ), and marble powder (MP) are used in ternary cementitious blends system following the cement substitution with PZ and MP in ratio 1/3. Within the framework of this experimental study, a total of 12 SCM and 6 SCC were prepared having a constant w/b ratio of 0.40. The fresh properties of the SCM were tested for mini-slump flow diameter, mini-V-funnel flow time, and viscosity measurement. Slumps flow test, L-box, J-ring, V-funnel flow time, and sieve stability were measured for SCC. Moreover, the development in the compressive strength was determined at 3, 7, 28, 56, and 90 days. Test results have shown that using ternary blends improved the fresh properties of the mixtures. The combination of natural pozzolana and marble powder increase the slump flow test up to 826 mm for the mixture prepared with 10% of mineral additions. Moreover, the use of mineral addition reduced the time flow to 4.27 s for SCC with 20% mineral addition, thus reducing the viscosity of all mixtures. Addition of MP increases the capacity of the passage through the plates between 88.75 and 93.50% for SCC with 7.5 and 15% of MP, respectively. The ternary system (PZ and MP) improve the sieve stability with the value for 4.07% of SCC with 50% of substitution compared for SSC without additions. The compressive strength of SCC at 90 days with 40% of PZ and MP was similar to that of OPC.

Analysis of Mortar Long-Term Strength with Supplementary Cementitious Materials Cured at Different Temperatures

This article will discuss an experimental study that was done to quantify the evolution of the mechanical strength modifications resulting from the presence of several supplementary cementitious materials (SCMs) in the mixture design of a mortar hardening under various curing temperatures. Mortars were made with various replacement levels of the cement by mass: 30 and 50% for slag; 10, 20, 30, and 40% for natural pozzolan; and 5, 15, and 25% for limestone powder. Samples were stored in a saturated-humidity moist room under various temperatures, namely 68, 104, and 140°F (20, 40, and 60°C). The results enable the verification of some hardening properties, such as half-strength age and long-term strength. The experimental results of half-strength age perfectly match with the previous studies that show a slower hydration of the cement with an increase in SCM. This effect decreases with the curing temperature. The long-term strength—depending on the curing temperature—is expressed by a parabolic expression contrary to the classical linear form in the case of ordinary portland cement (OPC). This new expression is more accurate in predicting the concrete longterm strength versus curing temperature with a part of cement replaced by SCM. Many experimental results obtained by other researchers have supported the proposed expression with a satisfactory accuracy, encouraging its generalization.

Rheology of ordinary and low-impact environmental concretes

This study deals with the rheological properties of concrete mixtures incorporating various types of mineral additions as a partial replacement of cement in order to produce a low-impact environmental concrete. The control mixture contained only Portland cement as the binder, while the remaining mixtures incorporated binary cementitious blends of slag, limestone filler, and fly ash with different rates of replacement. After mixing, the plastic viscosity and yield stress of the concretes were evaluated at different slump values using a rheometer apparatus. The results showed that the type of mineral additions and the rate of substitution affect the rheological parameters of low-impact environmental concrete. Indeed, increasing the degree of substitution leads to an increase in the plastic viscosity of the concrete made with different types of additions used in this study.

Effect of fine aggregate replacement with desert dune sand on fresh properties and strength of self-compacting mortars

This paper presents the results of an experimental study that investigated the rheological and mechanical properties of self-compacting mortars incorporating fine dune sand (DS), which has a tight Particle size distribution. Mortar mixtures were prepared with crushed sand (CS) or river sand (RS) in which the fine aggregates were replaced partially by different percentages of DS of 0, 25, 50, 75 and 100%. The effect of DS on the fresh mortars properties was studied using the mini-slump flow, V-funnel flow time and viscosity measurements tests. Compressive strength and flexural strength were determined at age of 3, 7 and 28 days. Experimental results indicate an improvement in fresh rheological without reducing in mechanical properties of self-compacting mortars when fine aggregates were replaced partially with DS (50%). However, at high-level DS replacement (75%) the slump flow decreases. The replacement of the DS to the CS or to the RS shows an increase in the mixture viscosity. In general, the compressive and flexural strength were not significant affected with an increase in DS replacement. Finally, based on the results obtained in this investigation, DS may provide a readily available alternative material as fine aggregates in mortar application.

The Compressive Strength of High-Performance Concrete and Ultrahigh-Performance

The compressive strength of silica fume concretes was investigated at low water-cementitious materials ratios with a naphthalene sulphonate superplasticizer. The results show that partial cement replacement up to 20% produce, higher compressive strengths than control concretes, nevertheless the strength gain is less than 15%. In this paper we propose a model to evaluate the compressive strength of silica fume concrete at any time. The model is related to the water-cementitious materials and silica-cement ratios. Taking into account the authors and other researchers’ experimental data, the accuracy of the proposed model is better than 5%.

Design of portable rheometer with new vane geometry to estimate concrete rheological parameters

AbstractThis paper presents the development of a portable vane rheometer to estimate concrete plastic viscosity and yield stress. The apparatus can be used not only in laboratory but also on construction site. In this study, new blade geometry was proposed to minimize the effect of segregation of concrete during testing, and also to expand the wide range of concrete workability with a slump of approximately from 7 cm to fluid concrete, and concrete with high plastic viscosity such as concrete with mineral additions. The used blade (U shaped and reversed) allows reducing the vibration of the apparatus, and obtaining more stable measurements. The obtained results permit validating the rheometer test procedure and confirmed that the results are reliable, with a low coefficient of variation of 9% for repetitive test and of 5.8% for reproductive tests.

Relationships between concrete composition and boundary layer composition to optimise concrete pumpability

Concrete pumpability is determined by the friction at the interface between the concrete and the wall of the pumping pipes (which are generally made of steel); called the concrete–steel interface. This friction is related directly to the thickness and composition of the boundary layer (BL) that occurs during the movement of fresh concrete in a pipe. These BL characteristics are rigorously linked with concrete composition parameters. To highlight this complicated relationship, an apparatus called a ‘tribometer’ was used in two experimental programs. This apparatus allows measurement of the steel–concrete interface friction and deduction of interface parameters (also called the pumping parameters), namely viscous constant and interface yield stress. The first program focuses on the effect of the concrete composition on pumping parameters, and the second program focuses on the relationships between the concrete composition and the BL composition. The results of the first program show that increases in cement paste volume, water/cement ratio and super-plasticiser dosage enhance concrete pumpability. Increased content of fine sand in concrete induces negative effects on the interface frictions and on the pumpability. The results of the second program show that the BL is formed by water, cement and fine sand particles with a diameter lower than 0.25 mm. It also shows that the proportions of water and cement volume in BL and micro-concrete (concrete with the largest grain diameter lower than 0.25 mm) are almost the same. The relative enrichment produced by fine sand in the BL decreases with increasing proportion of fine sand volume in the concrete. La pompabilité d’un béton est déterminé par le frottement à l’interface entre le béton et la paroi des tuyaux de pompage généralement en acier (appelé l’interface béton-acier). Ce frottement est relié directement à l’épaisseur et la composition de la couche limite (note BL) formée au cours d’écoulement du béton frais dans un tuyau de pompage. Ces caractéristiques de la BL sont rigoureusement liées avec les paramètres de composition du béton. Afin de mettre en évidence cette relation complexe, les auteurs ont utilisé dans ses deux programmes expérimentaux son appareil, qui a été récemment développé, appelé ‘tribomètre’. Cet appareil permet de mesurer les frottements à l’interface béton - acier et d’en déduire les paramètres d’interface (appelé aussi les paramètres de pompage), à savoir la constante visqueuse et le seuil d’interface. Le premier programme se focalise sur l’influence des paramètres de composition du béton sur les paramètres de pompage et le deuxième programme se focalise sur la relation entre la composition du béton et la composition de la couche limite. Les résultats du premier programme montrent que l’augmentation du volume de pâte, du rapport eau/ciment et du dosage en super-platifiant favorise la pompabilité du béton. L’augmentation du dosage en sablon substitué au sable de béton induit des effets négatifs sur les frottements et sur la pompabilité. Les résultats du deuxième programme prouvent que cette couche est constituée de l’eau, du ciment et des particules fines de sable du béton dont le diamètre est inférieur à 0,25 mm. Ils montrent également que la proportion volumique de l’eau et du ciment de la couche limite et du micro – béton (béton avec le plus grand diamètre des grains inférieur à 0,25 mm) sont presque identiques. L’enrichissement relatif en sable fin dans la couche limite diminue avec l’augmentation de la proportion volumique des fines de diamètre inférieur à 0,25 mm dans le sable béton.

Formulation and rheology of eco-self-compacting concrete (Eco-SCC)

Abstract This article presents the results of an experimental study on the rheology of eco-SCC, formulated on the basis of the modified Chinese method and on the new standard EN206/CN. The studied ecological concretes consist of Portland pozzolana cement, containing large amounts of limestone filler or natural pozzolana, which can replace cement up to 50%. In addition, the compactness of the granular mixture is optimized; therefore, the total amount of the incorporated binder is further reduced in the body of concrete. The study of the rheological behavior of these fluid concretes was carried out in the laboratory, using a coaxial vane-type rheometer. The results showed that both rheological models, i.e. modified Bingham and Herschel–Bulkley, describe satisfactorily the shear-thinning character of the formulations tested. However, the rheological parameters obtained with the modified Bingham model seem to have better correlations with the measurements of the slump test. These same results also indicated that replacing 30% of cement by one of the additions selected for our study, resulted in mixtures with yield stress and plastic viscosities that are within the validity range of SCC. This allowed reducing CO2 emissions by about 40% for each cubic meter of concrete produced.

Estimation of the Pumping Pressure from Concrete Composition Based on the Identified Tribological Parameters

A new method is proposed to estimate pumping pressure based on concrete composition without experimental measurements. Previous studies show that the pumping pressure depends on the interface friction between concrete and the wall of the pumping pipes. This friction is determined by the thickness and the rheology of the boundary layer formed at the interface. The latter is mainly formed by water, cement, and fine sand particles which come from concrete. Hence, interface parameters, which are the viscous constant and the interface yield stress, are directly related to concrete composition. In this work, at the first time the interface yield stress model is suggested and validated thanks to an experimental database also carried out in this study with a precision of around 13%. Then, the pressure estimation method is proposed using the two models to calculate the interface parameters. The validation of the method is carried out basing on the comparison with real measurements on the building site. This method enables the calculation of the pumping pressure with a precision of around 15%.