Papers by Keyword: Cementitious Material

Abstract: The technology of concrete greatly evolved in the recent years. The use of cements with a high dosage and the addition of fibres allowed a very compacted cementitious matrix. This fact may greatly affect the durability of a cementitious system. In this work, the durability of an ultra high strength fibre reinforced concrete was studied. The microstructure was dense, compact and exhibited a low capillary and total porosity as well as water permeability. Fluid resin penetration tests under pressure also showed a local difference in the penetration depth: from a thin surface layer to local small regions. Thus, the penetration potential of salts and water transporting degrading substances from the surface was reduced. The cement-based material was exposed to accelerated freeze/thaw and sulphate penetration tests, to clarify the durability and the capability of the low porous matrix to withstand the ingress of substances. In both cases the resistance was significantly higher as compared to conventional concrete. The crystalline quartz-rich matrix and the chemistry also played a relevant role in the low degradation of the system.

Abstract: The paper describes experiments designed to determine shrinkage in three types of self-levelling floor compounds. The research was designed as a double-comparative experiment. It compared shrinkage values between the flooring compounds as well as shrinkage measured on two different types of specimens. The shrinkage measurements were supplemented by the determination of weight losses. The flooring compounds discussed herein are defined by consistency and basic hardened-state properties. The measurements show the influence of specimen size on the progress and final value of shrinkage and weight losses.

Abstract: Geopolymer cement is an aluminosilicate material which activated by the alkaline solution. With appropriate heat curing regimes, geopolymer cement could achieve an excellent performance as construction material. Apart from that, geopolymer cement is one of the alternative cementitious materials for green construction as its raw starting materials could be any pozzolanic industrial by-products. Global carbon-dioxide emission from Portland cement consumption could be reduced with the replacement of that geopolymer cement. Therefore, the development of geopolymer cement is receiving much more attention. However, various kinds of materials have been used as geopolymer precursors. The main aim of this paper is, thus, to summarize current information on the usage of raw materials in geopolymer production by categorize its types and sources. The summarised details of chemical composition and compressive strength could provide a guide line for readers to evaluate possible reactions or outputs of their selected local raw materials as well as the prediction of material’s combination for the improvement of targeted strength of each possible prime material.

Abstract: Important deteriorations have been observed in concrete sewers, due to hydrogen sulfide (H₂S) production. Hydrogen sulfide environment involves the selection of sulfur-oxidizing bacteria (bacteria able to oxidize the reduced sulfur compounds) in contact with the cementitious materials. These biological reactions lead to a local production of sulfuric acid and, as a consequence, to the dissolution of cement matrix and its mineralogical transformations (gypsum and ettringite formation). This phenomenon disturbs the sewer system and leads to expansive works of rehabilitation. As a consequence, a project was initiated in order to propose more efficient solutions. The main objectives of this project are to set up an accelerated test and to develop an associated model. To date, experimental studies and some improvements of the model previously setting up were performed. The first study describes the impact of several parameters, including type of cementitious materials, on hydrogen sulfide adsorption. These abiotic tests involve monitoring hydrogen sulfide concentration as a function of time. This experiment was realized in a hermetic chamber with five types of mortars (cast with calcium aluminate cement (CAC), blended Portland cement (CEM III, CEM IV and CEM V) and super sulfated cement (SSC)) and under different relative humidity. The second study is deterioration state of mortars characterization, thanks to some analyses (SEM – EDX). After three months of exposition, different types of sulphur species are observed on mortar surfaces, which vary with the nature of mortar. All these experiments allow providing improvements to model previously setting up. Abiotic tests measurements are used to determine mathematical law, which modelises hydrogen sulphide adsorption on each type of cementitious material.

Abstract: Supplementary cementitious materials are most needed to enhance a sustainable development in poor communities. It is pertinent to investigate the suitability of such alternative materials for construction. The present study evaluates the strength characteristics of concrete made with varied proportion of Cordia millenii ash blended with Portland cement. Chemical composition of Cordia millenii and the setting time when blended with cement was determined. Other laboratory tests performed on Cordia millenii blended cement include: sieve analysis and specific gravity. Five replacement percentages of Cordia millenii (5%, 10%, 15%, and 20%) were blended with cement in concrete. Control specimens were also produced with only cement. Tests to determine the workability, air entrained, bulk density and compressive strength properties of the concrete were also conducted. Results obtained revealed that optimum Cordia millenii mix is 10%, which yielded the highest density and compressive strength in the concrete.

Abstract: This paper studied the cascade use of industrial waste slag as the cementitious material, the fine aggregate and the coarse aggregate, assisted by XRD, SEM and other microscopic test methods. The results that the system had the best volume stability when the steel slag addition of 40%. When the cement mortar prepared by 10% steel slag fine aggregate, and mixed with 20% steel slag powder and 20% blast furnace slag powder, the mortar construction performance and shrink resistant performance is excellent. On the basis of concrete double mixing 25% steel slag aggregate and 30% steel slag powder, compound mixing 20% blast furnace slag powder, the durable properties of concrete are also excellent.

Abstract: Dispersion of carbon fiber in cement matrix is one of main challenges for fabricating carbon fiber reinforced cement based materials. In this study, the dispersion of carbon fiber was improved by pre-dispersion of carbon fiber in basic aqueous solution using different concentrations of CMC. The relationships of CMC concentration and pH solution toward carbon fiber dispersion in aqueous solution was evaluated by UVvis spectroscopy. In order to understand how carbon fiber is dispersed in cement matrix, morphology fiber carbon reinforced composite was examined. Experimental results show that aqueous solution of CMC is effective to disperse carbon fiber. In addition, dispersion of carbon fiber increases with increasing of pH of CMC solution.

Abstract: Nanomaterials could change the face of modern construction because they are more resistant, more durable and have notable features. Concrete is a material widely used in construction industry worldwide. Carbon nanotube has been considered a new and outstanding material in nanoscience field with great potential application in the construction industry. The study presented in this paper, aims at assessing how carbon nanotubes can affect cement composites and so the concrete, in terms of microstructure and physical-mechanical properties. Three different ratios of carbon nanotubes have been searched: 0.20%, 0.40% and 0.60%. To evaluate the mechanical properties of the samples, destructive and non-destructive tests were carried out to obtain compressive strength, tensile strength by diametrical compression, dynamic modulus of elasticity as well as the determination of their deformation properties. This work also aims to motivate entrepreneurs and professionals in the sector of civil engineering on the advantages of the application of nanotechnology in construction, as well as providing information to the scientific and technological community in general.

Abstract: This paper presents the theoretical analysis of capillary absorption dynamics for cemementitious material. Fractal theory is applied to analyse tortuosity of capillary pores in cementitious material and a definition of tortuosity is given. The dynamic equation of capillary absorption considering water evaporation and tortuosity of capillary pores is derived. Based on the dynamic model, the capillary coefficient and sorptivity of concrete are explained theoretically. In absorption test, water evaporation is one of the main reasons caused variations from linearity between water absorption height and the square root of time, or between water amount absorbed and the square root of time. In cementitious material, the evaporation rate is very small compare to capillary flow velocity at the initial time of absorption test. For simplification of testing procedure, there is no meaning to modify absorption test.

Abstract: As the sign of social development, the vehicles and traffic flux have been increasing and have greatly influenced the ecological environment at the same time, especially on the cementitious based materials along roads as well as constructions. Heavy metal particle and ion absorption behavior and mechanism in cement materials were investigated and analyzed by means of ICP, SEM-EDS and XRD. The absorption mechanism was discussed and generalized.