Jean Ambroise

USE OF INCINERATOR BOTTOM ASH IN CONCRETE

The aim of the present work was to show if municipal solid waste incinerator (MSWI) bottom ash could be an alternative aggregate for the production of building concrete presenting a characteristic 28-day compressive strength of 25 MPa. The aggregates passing the 20-mm sieve and retained on the 4-mm sieve were considered for investigation. They showed lower density, higher water absorption, and lower strength than natural gravel. They could be considered as average quality aggregates for use in concrete. When directly introduced in concrete, they led to swelling and cracking of specimens, due to the reaction between cement and metallic aluminium. Therefore, a treatment by sodium hydroxide was proposed to avoid such degradation, which made possible the partial replacement (up to 50%) of gravel in concrete without affecting the durability.

Properties of Metakaolin blended cements

Abstract Metakaolin is a supplementary cementitious material with pozzolanic properties. Its activation by triacalcium silicate (C 3 S), triacalcium aluminate (C 3 A), and ordinary Portland cement is reported. The early hydration period of pastes containing metakaolin was investigated using isothermal calorimetry and conductivity. Differential thermal analysis, X-ray diffraction, and Fourier transform infrared spectrometry were used to follow the consumption of calcium hydroxide (CH) and identify the products of reaction. Compressive strength and porosity were also determined. The results show that CH is quickly consumed, the microstructure is rich in CSH and stratlingite (C 2 ASH 8 ), and the pore size distribution is displaced toward smaller values. Advanced Cement Based Materials 1994, 1, 161–168

Effects of different viscosity agents on the properties of self-leveling concrete

It has already been reported that a suitable quantity of welan gum, a kind of natural water soluble polysaccharide, is very effective in stabilizing the rheology of self-consolidating concrete. The main problem of this product is its cost. Therefore, new viscosity agents were investigated in the present study: starch, precipitated silica, and a waste from the starch industry. Associated with a sulfonated melamine-formaldehyde superplasticizer, these agents were used to develop self-leveling concrete at low cost (20% higher than that of concrete used in building construction). This paper presents the influence of the type of viscosity agent on various properties of concrete: workability, segregation, bleeding, compressive strength, shrinkage, and permeability. Precipitated silica and starch were found to lead to the best performances.

Hydration reaction and hardening of calcined clays and related minerals V. Extension of the research and general conclusions

Abstract For a comparison between the behaviour of pure metakaolinite and other clays or related minerals thermally activated at 750°C, the research has been extended to different calcined raw-materials, e.g. montmorillonite, illite, muscovite and phlogopite, impure natural clays, laterites and tropical soils, black colliery spoil and slate waste. The more reactive solids obtained by thermal activation are pure kaolinite and kaolinitic minerals such as tropical soils and laterites: the hydration of samples added with calcium hydroxyde and gauged at normal consistency leads to optimal 28 days strength from 15 to 27 MPa. Montmorillonite and illite lead to lower 28-days strength. Pure muscovite and phlogopite, black colliery spoil and slate waste do not present any interest in this field when thermally activated at 750°C. Some recommendations are given for a practical application of the research.

Development of a pozzolanic pigment from red mud

Red mud is a waste generated by the aluminium industry, and its disposal is a major problem for this industry. Very rich in iron, it can be used as cheap pigment for coloured concrete. The red coloration can be enhanced by calcination in the range of 600 to 800 °C. Such operation also transforms the aluminium hydroxides (goethite and boehmite) and clays minerals into pozzolanic admixtures that are able to consume the calcium hydroxide produced by cement hydration. Thus, it is possible to develop a new admixture for concrete: a pozzolanic pigment. The pozzolanic properties of calcined red mud were investigated by monitoring lime consumption of different mixtures of OPC and red mud. The main products of hydration were C-S-H and mono-carboaluminate (C4ACH11). A uniform and durable coloured concrete was obtained using white cement interground with 11% of burnt red mud.

Valorization of phosphogypsum as hydraulic binder.

Phosphogypsum (calcium sulfate) is a naturally occurring part of the process of creating phosphoric acid (H(3)PO(4)), an essential component of many modern fertilizers. For every tonne of phosphoric acid made, from the reaction of phosphate rock with acid, commonly sulfuric acid, about 3t of phosphogypsum are created. There are three options for managing phosphogypsum: (i) disposal or dumping, (ii) stacking, (iii) use-in, for example, agriculture, construction, or landfill. This paper presents the valorization of two Tunisian phosphogypsums (referred as G and S) in calcium sulfoaluminate cement in the following proportions: 70% phosphogypsum-30% calcium sulfoaluminate clinker. The use of sample G leads to the production of a hydraulic binder which means that it is not destroyed when immersed in water. The binder including sample S performs very well when cured in air but is not resistant in water. Formation of massive ettringite in a rigid body leads to cracking and strength loss.

Hydration reaction and hardening of calcined clays and related minerals. IV. Experimental conditions for strength improvement on metakaolinite minicylinders

Abstract For metakaolinite cements activated by calcium hydroxide, the more convenient curing process to optimize 28 days compressive strengths on pure paste minicylinders was defined as follows: samples are removed from the molds at 7 days, then cured in liquid water and tested after drying for one day at 50°C. In such conditions, strength values, which are about 10% lower than those measured on 4×4×16cm standardized prisms cured in the same way, become optimal with a metakaolinite/calcium hydroxide ratio of 3. They attain 26–27 MPa and 32–33 MPa when samples are gauged at normal consistency and at the limit of workability, respectively. The strength improvement depends on the nature of hydrates which form during the hardening, then on the curing process. It is essentially correlated to CSHI formation during the hydration reaction, the correlation becoming linear only at ages higher than 28 days. In one other hand, the hydration of metakaolinite with chemical activators other than hydrated lime (calcite, gypsum) has been investigated without any success.

FIBER-REINFORCED MAGNESIA-PHOSPHATE CEMENT COMPOSITES FOR RAPID REPAIR

Abstract Magnesia-phosphate cements are fast setting materials which can be used for rapid repair. While they are typically brittle in nature, their ductility can be significantly improved by addition of fibers. This paper presents some results obtained with five different types of fibers, namely E-glass, polyester, polypropylene, polyamide, and metallic. E-glass and polyester fibers are usually destroyed by chemical reaction with ordinary Portland cement but are compatible with magnesia-phosphate cement. The fiber volume fraction ranged from 0.69% (metallic) to 1.32% (polyamide). The composites were prepared according to the premix method, the matrix being composed of 50% magnesia-phosphate cement and 50% sand. The behavior of such composites was compared to that of a control composite made with ordinary Portland cement based composite reinforced by 0.97% A.R. glass fibers. Besides the type of fiber and cement matrix, the test parameters included the age at loading (from 3 h to 90 days) and the exposure conditions by prior immersion in hot water or by cycles of wetting and drying. Test results include the load-deflection response, the modulus of rupture, the toughness indices, the residual strength factor and a comparison of the various modes of failure. It is pointed out that the performance of magnesia-phosphate cement composites, at 3 h of age, was about the same as that obtained at 28 days by the control composite. Moreover, when subjected to accelerated aging, these composites maintained their performance, and elastic-plastic behavior in bending was observed as polypropylene and metallic fibers were used.

DEVELOPMENT OF AN ADMIXTURE FOR SELF-LEVELING CONCRETE

In the past decade, many efforts have been undertaken to develop highly-workable concrete which consolidates under its own weight without any vibration, specially in Japan. The admixtures used in such concrete are mainly composed of high water reducing superplasticizers, fine limestone dust and viscosity agents to maintain not only high flowability but high segregation resistance of the concrete. The water to cement ratio is generally lower than 0.55. A new admixture is proposed in the present study. It is a mixture of a superplasticizer and an accelerator with plasticizing properties which also acts as a viscosity agent. The composition of the self-leveling concrete is as follows. The total amount of fine materials (cement + fly ash or cement + ground limestone) is 370kg/m^3, while the cement content (normal portland cement CEMI 52.5) is 260kg/m^3. The water to cement ratio is 0.73. The mechanical performances of the hardened concrete is better than those of a usual French building concrete. The compressive strengths at 16 hrs, 7 days, and 28 days are 8, 30, and 3 MPa, respectively. The unrestrained drying shrinkage reaches 600 to 700mm/m, at 90 days as predicted from the 28 day results.

Microwave processing of glass-fiber reinforced composites—Modification of the microstructure

Abstract The present article deals with the influence of microwave treatment on the properties of glass-fiber reinforced composites. The cement used in the matrices of the composites was either plain ordinary portland cement or metakaolin-blended cement. Two levels of microwave power were investigated: 40 W and 80 W for 1 hour 30 minutes. The behavior of such composites was compared to that of specimens cured at ambient conditions (20°C) and at 60°C and 90°C. The mechanical behavior was assessed by means of three-point flexure tests. The microstructure was investigated using differential thermal analysis, infrared spectrometry, and scanning electron microscopy. The results obtained show that microwave treatment enhanced the pozzolanic reaction between ordinary portland cement and metakaolin and the bond between the fibers and the matrix. Interfaces between fibers and matrix were also modified. The mechanical performances of the microwave-processed composites were very interesting at early ages, but microwave heating degraded some long-term properties, such as work of fracture and toughness.