Miguel Ángel Sanjuán

Effect of low modulus sisal and polypropylene fibre on the free and restrained shrinkage of mortars at early age

This is the first part of a two-part paper involving the study of the free plastic shrinkage and cracking sensitivity during early drying of mortars reinforced with low modulus sisal, coconut, and polypropylene fibres. This work also evaluates the effectiveness of crack control at early ages on the corrosion of steel bars, which are sensitive to the presence of cracks in the matrix. The performance of cement-based material in the fresh state is expected to improve by reducing the free shrinkage and sensitivity to cracking due to the addition of a low content of polypropylene fibres. This paper discusses the effectiveness of the use of natural sisal fibres for controlling the free and restrained early age shrinkage of mortars and compares their performance with that of polypropylene fibre. In addition, a prediction model for the free plastic shrinkage of natural sisal fibre reinforced mortars is proposed based on a factorial design of experiment.

Effectiveness of Crack Control at Early Age on the Corrosion of Steel Bars in Low Modulus Sisal and Coconut Fibre-Reinforced Mortars

Abstract This is the second part of a two-part paper involving the study of the free plastic shrinkage and cracking sensitivity at early drying of mortars reinforced with low modulus sisal and coconut fibres, and the evaluation of the effectiveness of crack control at early age on the corrosion of steel bars, which is sensitive to the presence of cracks in the matrix. The incorporation of fibres in the mortar is proposed to control cracking and, therefore, to provide a more homogeneous composite material. Whether such addition improves the compactness of the mortar by reducing crack propagation at early age and the corrosion of the embedded steel bars with time is the subject addressed in the present work. Mortar samples with reinforcing bars were submitted to early drying after casting, to develop cracks in the vicinity of the rebars, and then held at 100% RH and room temperature until 40 days when they were exposed to a chloride solution to enhance the corrosion rate of the steel bars. The corrosion of the steel bars was monitored by electrochemical measurements and observations of crack development. Natural fibres perform well in controlling cracking in mortars and also seem to delay slightly the initiation of the corrosion of embedded steel bars. Self-healing of cracks is more effective in smaller ones and, therefore, in natural fibres, reinforced mortars present a higher self-healing behaviour.

Coal Bottom Ash for Portland Cement Production

Because of industrialization growth, the amount of coal power plant wastes has increased very rapidly. Particularly, the disposal of coal bottom ash (CBA) is becoming an increasing concern for many countries because of the increasing volume generated, the costs of operating landfill sites, and its potential hazardous effects. Therefore, new applications of coal bottom ash (CBA) have become an interesting alternative to disposal. For instance, it could be used as a Portland cement constituent leading to more sustainable cement production by lowering energy consumption and raw material extracted from quarries. Coal fly and bottom ashes are formed together in the same boiler; however, the size and shape of these ashes are very different, and hence their effect on the chemical composition as well as on the mineralogical phases must be studied. Coal bottom ash was ground. Later, both ashes were compared from a physical, mechanical, and chemical point of view to evaluate the potential use of coal bottom ash as a new Portland cement constituent. Both ashes, produced by the same electrical power plant, generally present similar chemical composition and compressive strength and contribute to the refill of mortar capillary pores with the reaction products leading to a redistribution of the pore size.

EVALUACIÓN DE UN NUEVO CONSTITUYENTE DEL CEMENTO PORTLAND: CENIZA DE FONDO MOLIDA

Coal bottom ash is produced in electrical power stations as result of the coal combustion. Because coal fly ash and coal bottom ash are formed together in the same boiler, similar chemical and mineralogical composition is expected. The size and shape of these ashes is very different, and then, its effect on the performance must be studied. In order to get a similar grain size to that of the coal fly ash, the coal bottom ash was ground. Cement-based products are the main construction materials which manufacture requires the use of significant natural raw materials and energy. These manufacturing processes result in several types of emissions. In particular, the cement industry is under pressure to reduce CO2 emissions and some studies have shown different measures to reach CO2 reduction. For instance, reducing the clinker/cement factor will lead to a clear CO2 emission reduction. In this work, ground coal bottom ash is investigated to know its viability of being used as a new Portland cement constituent. Then, it is studied from a mechanical and durability point of view to evaluate the potential use of the coal bottom ash as an innovative binder. Ground coal bottom ash and fly ash mortars were more carbonated and exhibited a lower compressive strength than the reference mortars, but similar to each other. Keywords: coal bottom ash, Portland cement, Compressive strength, Durability

Modeling of Corrosion Rate and Resistivity of Steel Reinforcement of Calcium Aluminate Cement Mortar

Calcium aluminate cement (CAC) is a binder whose hydrated compounds change over time from cubic phases to hexagonal phases, producing an increase of porosity in reinforced concretes. Thereby, chloride ions, among other steel corrosion promoters, can enter the concrete more easily leading to an increase of the reinforcement corrosion process. When such a transformation of phases is completed, a characteristic value regarding both corrosion intensity (Icorr) and resistivity (related to the ohmic drop of the cementitious material) is reached, which depends mainly on the mix proportions of the material and the curing procedure. This paper presents the characteristic corrosion intensity values of steel embedded in mortars made of CAC after five years of exposure to either a 0.5 mol/l or 1.5 mol/l NaCl solution in order to be applied to estimate the service life of reinforced concrete made of calcium aluminate cement (CAC) which is used in real construction structures. Ohmic drop measurements are also presented to support the values obtained. The aim of this paper is to model the corrosion rate and resistivity of the steel reinforcement of calcium aluminate cement mortar with regard to environmental factors (temperature and chloride content) and mortar quality (water/cement ratio).

Coal bottom ash natural radioactivity in building materials

The viability of ground coal bottom ash as a potential Portland cement constituent to be used in building materials is assessed. Currently, coal fly ash is used to produce Portland cements and concretes. However, coal bottom ash is mainly landfilled. Gamma spectrometry analysis, compressive strength, physical and chemical testing were performed. The ground coal bottom ash activity concentration index (I = 1.03) was compared to that of the coal fly ash (I = 1.11) provided from the same thermo-electrical power plant. Ground coal bottom ash could be used in building materials in the same way as coal fly ash as a Portland cement constituent.