HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

This paper investigates the influence of the content of blast furnace slag (BFS) on the microstructural and mechanical properties of non-activated and activated ultra-high performance concrete (UHPC). Three volume-substitution rates of cement with BFS were explored (30% for UHPC 2 , 50% for UHPC 3 and 80% for UHPC 4) and two activation methods, chemical and thermal, were tested. Results show that with 30% of BFS, heterogeneous nucleation prevailed over dilution, accelerating the hydration reaction of cement and increasing the amount of C-S-H formed. C-S-H decreased the porosity of UHPC 2 by 18% and 20% respectively at 3 and 90 days. The compressive strengths of UHPC 1 (without BFS) and UHPC 2 were very similar. For high BFS contents, the dilution effect prevailed and there was less portlandite, which decreased the amount of hydrated products, particularly at early age. As a result, the porosity of UHPC 3 and UHPC 4 was more than twofold higher than that of UHPC 1. To boost the hydration reaction of blended UHPC with a high BFS content, KOH was added. The use of [KOH] 3 significantly increased the amount of hydrated products, reducing the porosity of UHPC 4 1.6-fold at 3 days and increasing its compressive strength by 42% at the same age. However, this activation mode was not enough to ensure the required compressive strength of UHPC 1. Thermal activation at 90°C for 2 days was therefore tested. Results showed the acceleration of the reaction of solid components, which increased the consumption of portlandite and hence the development of hydrated products. This resulted in improving the packing density of blended UHPC, decreasing its porosity and enhancing its compressive strength. In comparison with reference concrete at 90 days, the compressive strength of UHPC 3-T increased by 7% and that of UHPC 4 was 12.5% lower.

This research examines the potential of using cement kiln dust (CKD) as a blended cement material to study the effects of this partial replacement on the most important properties of cement paste, mortar and concrete. The levels of replacement of cement by an equal amount of the (CKD) dust were (5, 10, 15, 20, 25, 30)% by weight. A reference cement paste, mortar and concrete mix were also prepared for comparison. The tested properties included the initial setting time of each cement paste and the compressive and tensile strengths of mortars and concrete. Water curing was used for all specimens and the strength tests were carried out at (3, 7, 28) days. Results of experimental data reveal that (CKD) can be effectively used as a partial cement material. The initial setting time of the cement paste is decreased with the increase of (CKD) content due to the high amount of lime and alkalis in (CKD). Besides, the compressive and tensile strengths of the blended cement and concrete specimens were also found to be comparable to the strengths of the reference mixes at all levels of replacement. Generally, it was indicated that the compressive strength decreased with the increase of (CKD) content. The (10)% replacement level had the best results in the compressive strengths of mortars and concretes at all ages in comparison to the reference mixes, also this level of substitution had a significant effect on the tensile strength of the mortars and concretes at early ages. It was noted that (15)% (CKD) replacement maintained the higher tensile strength of mortars at (7, 28) days, whereas a (25)% (CKD) had a similar effect but at (3, 28) days.

This research work includes an experimental investigation to study the effect of high temperatures on the mechanical properties of concrete containing admixtures. A comparative study was conducted on concrete mixes, reference mix without an additive and that with an admixture. Concrete was exposed to three levels of high temperatures (200,400,600)°C, for a duration of one hour, without any imposed load during the heating. Five types of admixtures were used, superplasticizer, plasticizer, retarder and water reducing admixture, an accelerator and an air entraining admixture. Mechanical properties of concrete were studied at different high temperatures, including: compressive strength, splitting tensile strength, modulus of elasticity and ultimate strain. Test results showed a reduction in the studied properties by different rates for different additives and for each temperature, the decrease was very limited at temperature up to (200°C) but was clear at (400,600)°C.

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The rehabilitation and reconstruction works are usually performed with a view to conserving these landmarks and maintaining them culturally, architecturally and structurally. From this perspective, the mortars utilized in these repairs must be suitable, physiochemically and mechanically, to the ancient materials used in these buildings. Accordingly, it was proposed to evaluate tufa stone powder, a waste product of one of the most widely found stones in the Loire Valley in France, as an ingredient in repair-work mortar mixtures (M1, M2) through partially replacing the fine aggregate it contains with different amounts of this powder (37%, 42%) by weight of mix. Additionally, a third manufacturing mortar (M3) was utilized with both prepared mortars (M1, M2) for comparison with the tufa stone. The mechanical properties (including flexural, compressive and shear strengths, and ultrasonic pulse velocity) and the durability properties (total porosity, thermal dilation and conductivity, capillary absorption, and water and gas permeability) of the three mortars were examined in addition to those of the tufa stone. The results revealed that the prepared mortar, M2, (having lower binder content and a higher amount of substitution with tufa stone powder) has the lowest mechanical performance in comparison with the other mortars, indicating that this mortar is more supple and loose than the authentic tufa masonry. The thermal and durability properties are comparable to that of the tufa stone existent in ancient monuments. Consequently, the prepared mortar (M2) is the most appropriate mortar, for utilization in repairing old landmarks in the Loire Valley in France.

Use of polypropylene fibers to reinforce concrete has attracted widespread attention from both researchers and construction industry because of the numerous characteristics they have, compared to other types of fibers. This paper critically reviews the current state of knowledge of impacting the inclusion of polypropylene fibers on concrete durability. Detailed review on the different durability properties including: Water and gas permeability, sorptivity, water absorption, chloride diffusion, carbonation, and frost resistance. The influence of polypropylene fibers on these properties is discussed in this paper.