Arezki Tagnit-Hamou

PERFORMANCE CHARACTERISTICS OF CEMENT GROUTS MADE WITH VARIOUS COMBINATIONS OF HIGH-RANGE WATER REDUCER AND CELLULOSE-BASED VISCOSITY MODIFIER

Abstract Cellulose-based viscosity-modifying admixtures (VMA) are used to increase the viscosity of cement-based systems, hence, reducing the risk of material separation during handling and transport and thereafter until the onset of hardening. To ensure proper fluidity such admixtures are incorporated along with high-range water reducers (HRWRs). The ability of the VMA to ensure the required rheological properties depends on the type and interaction with the incorporated HRWR. Good understanding of such interaction is essential to ensure adequate performance. Limited knowledge is available on the effect of cellulose-based VMA and HRWR on physico-chemical characteristics and cement hydration. The performance of grouts made with 0.40 water/cement (w/c) ratio containing a liquid-based cellulose material was investigated for mixtures made with polynaphtalene sulfonate (PNS) and polymelamine sulfonate (PMS) HRWR. The grouts are tested for fluidity, rheological properties, stability, setting and rate of hydration. The grouts were also tested for strength and pore-size distribution, and microstructural characteristics. This paper summarizes the results of the study regarding the influence of the type and dosage of HRWR on key characteristics of grouts made with the cellulose-based VMA.

Pore structure of concrete with mineral admixtures and its effect on self-desiccation shrinkage

High-performance concrete (HPC) is known for the specificity of its pore system compared with that of conventional concrete. Indeed, its capillaries are characterized by very fine pores. Refinement of these pores mainly depends on the type, proportion, and fineness of the pozzolanic materials incorporated. The finest HPC pores, however, induce two opposite phenomena: on the one hand, better mechanical performances, which lead to considerable improvement in durability; and on the other hand, increased self-desiccation shrinkage caused by the high capillary depression in these finer pores. This study highlights both fundamental aspects resulting from the use of mineral admixtures in HPC. Concrete mixtures with two water-binder ratios (w/b) of 0.35 and 0.30, and three types of binders were used in this research. Shrinkage was measured on massive blocks that somewhat simulated a real concrete structure. The pore size distribution was measured at different ages by mercury intrusion porosimetry (MIP). The results obtained show that refinement of the capillary network and its evolution with time are closely related to mineral addition type and fineness. Moreover, refinement of the pores evolves significantly at a very early age depending on the type of binder used. This change in the pore structure of capillaries induces an increase in the magnitude of self desiccation shrinkage during this lapse of time. Also, the lower the w/b of the mixtures, the higher the effect of refinement of the capillary network on self desiccation shrinkage development. It was also found that the incorporation of mineral admixtures considerably reduces the average pore radius while it increases the amount of pores smaller than 15 nm (5.9 x 10 ―7 in.). In general, the smaller the average pore radius is, the higher the shrinkage will be.

IS MICROCRACKING REALLY A PRECURSOR TO DELAYED ETTRINGITE FORMATION AND CONSEQUENT EXPANSION

Several previous studies have shown the importance of the pre-existence of microcracks to delayed ettringite formation (DEF) and consequent expansion. Other research results, however, showed clear differences of expansion behavior depending on the causes of microcracks. This article reports on a study of the expansion of 40 and 36 heat-cured mortar and concrete mixtures, respectively. The ultimate value of expansion due to DEF is always higher for slow-cooled samples than this same value for rapid-cooled samples. The thermal shock of rapid-cooled samples creates microcracks. However, the authors conclude from their results that microcracking caused by thermal shock does not promote expansion. On the contrary, this type of microcracking decreases the ultimate value of expansion, though it can accelerate it because microcracks facilitate the availability of water.

Application of new information technology on concrete: an overview

Abstract The development of information technology provides means for quick access to a wide variety of information and methods of modelling complex systems. Simulation models, databases, decision support systems and artificial intelligence have currently become more accessible. Advances of these techniques continue to impact highly on civil engineering. The aim of this paper is to present recent developments in information technology and their influence on concrete technology. A historical perspective on researches and a review of the application of artificial intelligence techniques on concrete are presented. Development of computer integrated knowledge systems, approach of virtual systems and soft- ware for concrete mix design are also discussed. These systems have greatly affected handling tasks in civil engineering design over the past decade and promise to have revolutionary impacts on the nature of the design tasks in the future. They are considered useful and powerful tools which are able to solve...

Durability of Alkali-Activated Slag Concretes Prepared Using Waste Glass as Alternative Activator

Concrete is by far the most used building material in the world, but is facing a large environmental challenge due to its cement content. The production of portland cement is responsible for 5 to 8% of worldwide CO₂ emissions. Waste and supplementary cementing materials (SCMs) such as blast-furnace slag can be used as partial or total substitute for portland cement to avoid or to reduce this negative effect. This work explores the study of durability and the mechanical behavior of concretes using urban and industrial waste glasses as a potential alkaline activator for slag (AAS). The development of strengths and microstructure in the concretes activated with waste glass were also comparable to the parameters observed in AAS concretes prepared with conventional activators. Durability tests, including chloride penetration resistance, freezing-and-thawing resistance, carbonation, resistivity, and porosity, were conducted and the effect of the different parameters such as the activator type is discussed.

Evaluation of Rate of Deformation for Early-Age Concrete Shrinkage Analysis and Time Zero Determination

Early age cracking is usually the result of internal tensile stresses induced by self-desiccation shrinkage (SDS) rather than external loading. Hence, the prediction of early age cracking risk is strongly linked to autogenous shrinkage development. Both the ultimate magnitude of shrinkage and the time zero (TZ), at which shrinkage starts to develop an internal stress, could be decisive for high-performance concrete (HPC) durability. The moment TZ can be considered as the borderline between autoplastic shrinkage and effective shrinkage. Deformation rate curves might be used as a framework to identify the three main phases of hardening that occur in cement paste as hydration progresses, and the development rate of autogenous shrinkage (AS). The present study proposes starting shrinkage measurement (autogenous or total) from the moment when the rate of deformation reaches its maximum value (the first peak in the curve) and the shrinkage strain rate curve pattern changes sharply, or at the end of plastic-shri...

Prediction of Efficiency Factor of Ground-Granulated Blast-Furnace Slag of Concrete Using Artificial Neural Network

The relative performance of various supplementary cementitious materials (SCMs) can be compared with that of portland cement using the practical concept of the efficiency factor (or χ value). This study describes the use of artificial neural networks (ANNs) for the prediction of the efficiency factor of ground-granulated blast-furnace slag (GGBFS) in concrete based on published test results. Feed-forward back-propagation neural networks have been used. The ANN model was established by the incorporation of a large experimental database and by appropriately choosing the architecture and training process. The introduced ANN model provided a more accurate tool to calculate χ and capture the effects of five main parameters: concrete composition (the waterbinder ratio [w/b]; cement dosage; and the GGBFS replacement level); age; and curing temperature, confirming the reported experimental data. This study shows that the use of this model for numerical investigations on the parameters affecting the efficiency of SCMs in concrete is successful. A mathematical model was also developed based on the ANN model’s results for predicting the χ value of GGBFS in terms of percentage replacement (from 0 to 80%) and concrete age (from 2 to 90 days), as these are considered the most important factors affecting concrete strength. This evaluation makes it possible to design GGBFS concretes for a desired strength at any given age and replacement level.

Impact of Alternative Cementitious Material on Mechanical and Transfer Properties of Concrete

An experimental program was carried out to characterize the risk of corrosion in reinforced concretes designed with alternative cementitious materials (ACMs). The study focuses on three alternative cementitious materials used with ordinary portland cement: glass powder (GP) obtained from mixture glass, alternative fly ash (AFA) obtained from the combustion of wastepaper deinking sludge and wood residues in a fluidized-bed reactor, and limestone filler (LF). Concrete specimens casted with water-binder ratios (w/b) of 0.4 and 0.55 were tested to determine compressive strength, chloride ion penetration, chloride diffusion, and porosity accessible to water. Reinforced concretes were also submitted to accelerated corrosion tests. The use of GP in replacement of cement increases resistance to chloride ion penetration. In this case, a low level of chloride ion penetration is maintained despite the increase of w/b. Hence, measurements of chloride ion penetration do not correlate with compressive strength values. The AFA improves resistance to the chloride ion penetration, particularly at high w/b, while the use of limestone filler has no significant impact. The chloride ion penetration tests show a good relation with the accelerated corrosion tests.

Structural Behavior of Concrete Incorporating Glass Powder Used in Reinforced Concrete Columns

AbstractBinary and ternary binders are recommended for the production of concrete mixes used in infrastructure because these concretes are environmentally friendly. Moreover, concrete produced by using glass powder (GP) as a binder shows very low permeability to chloride ions. An extensive research project on the use of GP as cementitious material is underway at the University of Sherbrooke, Quebec, Canada. The northeastern Canadian province of Quebec has a policy on waste management to promote the recovery and management of materials from the municipal, industrial, commercial, and institutional sectors. Therefore, new alternatives for using recycled glass are needed. GP contains approximately 70% silicon dioxide. Thus, the replacement of 20% of cement with the incorporation of GP into the formulation of concrete provides economic and environmental benefits. Moreover, it has been shown that concrete with 20% GP has a very low permeability to chloride ions, which makes it a suitable solution for RC element...

Durability and Testing – Chemical Matrix Degradation Processes

This chapter, and the two that follow, are structured to provide an overview of the available test methods for assessment of the performance of construction materials under a wide variety of modes of attack. These are divided, broadly, into ‘chemical’ (Chap. 8), ‘transport’ (Chap. 9) and ‘physical’ (Chap. 10) – and it is noted that this classification is to some extent arbitrary, with a significant degree of crossover between the three categories which is difficult to take explicitly into consideration in a format such as this. Some areas are discussed in far more detail than others, either because they are critical points related to certain areas of alkali-activation technology, or sometimes simply because limited information is available regarding some forms of attack on alkali-activated materials (AAMs); biologically-induced corrosion is one such case, where very little information is available in the open literature. These chapters will in general raise questions for future consideration rather than providing detailed answers, due to the limited state of understanding of AAM degradation mechanisms at present, although recommendations will be drawn wherever possible.