Showing papers on "Mortar published in 2003"

Development of vegetable fibre–mortar composites of improved durability

Abstract: The primary concern for vegetable fibre reinforced mortar composites (VFRMC) is the durability of the fibres in the alkaline environment of cement. The composites may undergo a reduction in strength and toughness as a result of weakening of the fibres by a combination of alkali attack and mineralisation through the migration of hydration products to lumens and spaces. This paper presents several approaches used to improve the durability performance of VFRMCs incorporating sisal and coconut fibres. These include carbonation of the matrix in a CO2-rich environment; the immersion of fibres in slurried silica fume prior to incorporation in the ordinary Portland cement (OPC) matrix; partial replacement of OPC matrix by undensified silica fume or blast-furnace slag and a combination of fibre immersion in slurried silica fume and cement replacement. The durability of the modified VFRMC was studied by determining the effects of ageing in water, exposure to cycles of wetting and drying and open air weathering on the microstructures and flexural behaviour of the composites. Immersion of natural fibres in a silica fume slurry before their addition to cement-based composites was found to be an effective means of reducing embrittlement of the composite in the environments studied. Early cure of composites in a CO2-rich environment and the partial replacement of OPC by undensified silica fume were also efficient approaches in obtaining a composite of improved durability. The use of slag as a partial cement replacement had no effect on reducing the embrittlement of the composite. © 2002 Published by Elsevier Science Ltd.

Development of Bottom Ash as Pozzolanic Material

Abstract: This research studies the potential of using bottom ash from the Mae Moh power plant in Thailand as a pozzolanic material. Bottom ash, which was rarely used in concrete due to its inactive pozzolanic reaction, improved its quality by grinding until the particle size retained on Sieve 325 was less than 5% by weight. Bottom ashes before and after being ground were investigated and compared for their physical and chemical properties. The bottom ashes were used to replace portland cement type I in mortar and concrete mixtures. The results indicated that the particle of bottom ash was large, porous, and irregular shapes. The grinding process reduced the particle size as well as porosity of the bottom ash. Compressive strengths of mortar containing 20–30% of bottom ash as cement replacement were much less than that of cement mortar at all ages, but the use of ground bottom ash produced higher compressive strength than the cement mortar after 60 days. When ground bottom ash was used at a 20% replacement of cemen...

Rheology of Particle Suspensions: Fresh Concrete, Mortar and Cement Paste with Various Types of Lignosulfonates

Abstract: The major issue concerns how the different lignosulfonate types changes the rheological properties of the cement based material (concrete, mortar and cement paste) as a function of temperature and ...

Effect of magnetic field treated water on mortar and concrete containing fly ash

Abstract: This research investigates the workability and compressive strength of mortar and concrete, which were mixed with magnetic field treated water (MFTW) and contained fly ash. MFTW was obtained by passing tap water through a magnetic field. Test variables included the magnetic strength of water, fly ash content in place of cement, water-to-cementitious material ratio (W/CM) and curing age. Results show that the compressive strength of mortar samples mixed with MFTW is higher than those prepared with tap water. The best compressive strength increase of concrete is achieved when the magnetic strength of treated water is of 0.8 and 1.2 T. The compressive strength increase of concrete prepared with MFTW is more significant at early age.

Microstructural investigation of a silica fume–cement–lime mortar

Abstract: Several additions, minerals and organic, are used in mortars, such as pozzolanic materials, cementicious materials and polymers. Literature about the use of additions in masonry mortars (cement/lime/sand mixes) is scarce; usually, studies are about concrete mortars. The purpose of this work is to study the microstructural effects of the substitution of 10% of Portland cement by silica fume in a 1:1:6 (cement/lime/sand mix proportion by volume) masonry mortar. Scanning electron microscopy with energy dispersive X-rays analysis (SEM/EDX) shows that, with silica fume, the C–S–H formed is type III at early ages and that type III and type I coexist at later ages. Silica fume lowers the total porosity and increases compressive strength only at later age and, as expected, the pore structure of mortar with silica fume is found to be finer than of non-silica fume mortar.

Fracture processes of hybrid fiber-reinforced mortar

Abstract: Subregion Scanning Computer Vision (SSCV), a digital image based method for measuring surface deformation is used to examine the role of the fibers in the fracture process of mortars reinforced with hybrid blends of microfiber (less than 22 μm in diameter) and macrofiber (500 μm in diameter). Closely-spaced microfibers interact with cracks at the microstructural level and hamper the widening of coalesced microcracks, thus encouraging the growth of multiple cracks. The microfibers improved pre-peak mechanical performance and strength by delaying the formation of a through-specimen macrocrack. Macrofibers were most effective at bridging macrocracks and imparting ductility to the composite due to their geometry and greater length. Compared to mortar reinforced with a single fiber type, an increase in strength and toughness was seen with a blend of steel macrofibers and either steel or PVA microfibers. Finally, based on the crack topography observed, the reduction in water permeability of cracked mortar achieved with hybrid fiber-reinforcement, measured directly in a parallel study, was governed by multiple crack development.

Study and characterization by acoustic emission and electrochemical measurements of concrete deterioration caused by reinforcement steel corrosion

Abstract: The durability of reinforced concrete structures becomes a matter of concern, due primarily to the increase of damage by the corrosion of steel reinforcements. This corrosion is not only related to the composition and to the procedure of concrete manufacturing (water/cement, sand/cement, etc.), but also to the aggressive agents as chlorides, carbon dioxide, etc. present in the surrounding medium (Cl − , CO 2 , etc.). It is well known that the first kind of rebar corrosion (chloride) is more detrimental and that this process contains three basic components: chloride diffusion, electrochemical corrosion and concrete fracture. Therefore the early detection of possible degradation of structures by means of non-destructive testing is essential in order to ensure the functionality of these structures. This paper presents the results of an experimental investigation on the use of acoustic emission during the corrosion of steel rebars embedded in mortar and immersed in sodium chloride solution. The process of corrosion is accelerated by various imposed potentials and is followed by acoustic emission coupled to electrochemical techniques. The experimental results show that electrochemical techniques can evaluate the corrosive character of the medium used. The acoustic emission showed an activity characteristic of the corrosion initiation phase and the corrosion propagation phase. Thus, it was significantly possible to highlight the acoustic signature of the concrete damage related to the porosity of the mortar and to chloride concentration. The results also show a perfect correlation between the evolution of the acoustic activity and the current of corrosion density.

Long term durability of Portland-limestone cement mortars exposed to magnesium sulfate attack

Abstract: Mortar prisms made with Portland-limestone cement have been stored in air and in 1.8% magnesium sulfate solution at 5 °C and have been examined over a period of 5 years. This paper is primarily concerned with the results obtained at the end of this period. The limestone content in the samples varied from 0% to 35%, but the water to cement plus limestone powder ratio was kept constant. The status of the samples after storage for 5 years is reported based on visual examination and a thorough characterisation using X-ray diffraction, infra-red spectroscopy and scanning electron microscopy. The prisms stored in magnesium sulfate solution were all showing clear signs of deterioration, increasing in intensity with limestone content. The mortar prism with 5% limestone replacement was, however, seriously degraded in comparison with the ordinary Portland cement control prism, and it is shown that this was due to the thaumasite form of sulfate attack.

The reuse of municipal solid waste incinerator fly ash slag as a cement substitute

Abstract: The results of the treatment of fly ash from a municipal solid waste incinerator (MSWI) by melting are described, and the safety and the effectiveness of using the slag produced by this melting treatment are studied. The properties of the MSWI fly ash slag were analyzed, to evaluate the feasibility of its reuse as a substitute for part of the cement required in mortar preparation. This MSWI fly ash slag was found to be comprised mainly of SiO2 and CaO, which can be substituted for up to 20% of the cement content in mortar, without sacrificing the quality of the resultant concrete. In fact, the concrete thus produced has greater compressive strength, 10% higher than that without the substitution. The setting time of the fresh mortar becomes lengthens as increasing amounts of cement are replaced; while the spread flow value increases with the increasing percentage of cement substitution. X-ray diffraction analysis reveals that when the W/C=0.38 and the curing age=28 days, the crystal patterns in the mortar samples, prepared with different amounts of cement having been replaced by MSWI fly ash slag are similar. According to the results of the toxic characteristic leaching procedure analysis, MSWI fly ash slag should be classified as general non-hazardous industrial waste, that meets the effluent standard. Therefore, the reuse of MSWI fly ash slag is feasible, and will not result in pollution due to the leaching of heavy metals.

ASR Potentials of Glass Aggregates in Water-Glass Activated Fly Ash and Portland Cement Mortars

Abstract: The purpose of the present study was to use two solid wastes—fly ash and mixed color waste glass—as constituents in concrete materials. The fly ash with water glass as activation chemical was used as a binder in the concrete, and the waste glass particles were used as aggregate to replace nature aggregate. The present study focused on the potential of alkali-silica reaction (ASR) of glass aggregates used in portland cement mortar and in water-glass activated fly ash (WAFA) mortar. The ASR potential was examined using the accelerated testing method, ASTM C-1260. The results showed that with 10% substitution of natural aggregate by glass particles, the ASR expansion of portland cement mortar depends on the size of glass aggregate. The ASR expansion of WAFA mortar does not depend on the sizes of glass aggregate but on the content of glass aggregate. The ASR expansion of WAFA mortar was below the critical ASR expansion up to 100% of replacement by glass aggregate. The color of glass does not affect the ASR potential of WAFA mortar.

Aggregate/mortar interface: influence of silica fume at the micro- and macro-level

Abstract: Microstructural investigations and chemical analyses were conducted by utilizing scanning electron microscopy and energy dispersive X-ray analyser in the interfacial zone between three types of cylindrical aggregates (sandstone, limestone and granite) and two types of mortar matrices (plain mortar and 20% silica fume mortar). The strength of the interface was determined experimentally by means of aggregate push-out test. Interfacial strength was then related to the interfacial thickness and the amount of silica at the interface. It was found that the higher the silica concentration in the interface, the thinner the relative interfacial thickness and the higher the interfacial bond strength as a result of the densification role of silica fume. The interfacial bond strength was found to increase as the aggregate size decreased, irrespective of the type of aggregate and the mortar matrix. This size effect is shown to be statistical in nature and described by Weibull theory.

Experimental study on enhancement of self-restoration of concrete beams using SMA wire

Abstract: Shape Memory Alloys (SMA) exhibit stable superelasticity between a reverse transformation finish temperature (Af) and approximately 30°C above Af, and therefore can sufficiently work as a superelastic material for structural use in building under the temperature in a construction environment. In order to verify the potential self-restoration capacity of mortar beams containing superelastic SMA reinforcements, static loading tests were conducted, and the results were then compared with those for a beam containing steel wires. The comparison indicates that (1) after maximum deflection, the mortar beam with SMA can return to an about one-tenth deflection compared with the maximum, (2) the range of deflection of the mortar beam with SMA is more than seven times that of the beam with steel, and (3) wide single crack can occur at the critical section due to a weaker bond force between SMA and mortar.

Determination of Early Age Mortar and Concrete Strength by Ultrasonic Wave Reflections

Abstract: The in situ testing of early age concrete strength is crucial for determining the time of form removal from concrete elements, opening highways to traffic, or applying prestress to steel reinforcement. A nondestructive ultrasonic technique, which measures the reflection loss of ultrasonic transverse waves at a concrete-steel interface, is presented in this paper. The aim is to compare wave reflection measurements on mortar and concrete to strength. It is shown that the reflection loss is linearly related to the strength gain of mortar and concrete at early ages. The experiments have revealed a relationship between the homogeneity of the tested materials and the consistency of the reflection measurements. The repetition of simultaneous measurements of wave reflections and compressive strength on mortar results in similar strength-reflection loss relationships. Multiple measurements on the same concrete gave multiple strength-reflection loss relationships. The accuracy of the strength predictions made with the proposed method is discussed and compared to that of other nondestructive test methods.

The use of oil shale ash in Portland cement concrete

Abstract: An experimental investigation was undertaken to study the potential use of Jordanian oil shale ash (OSA) as a raw material or an additive to Portland cement mortar and concrete. Different series of mortar and concrete mixtures were prepared at different water to binder ratios, and different OSA replacements of cement and/or sand. The compressive strength of mortar and concrete specimens, cured in water at 23 °C, was determined over different curing periods which ranged from 3 to 90 days. The results of these tests were subjected to a statistical analysis. Equations were developed by regression analysis techniques to relate the effect of batch constituents on the strength developments of OSA mortars and concretes. The models were checked for accuracy by comparing their predictions with actual test results. The obtained results indicated that OSA replacement of cement, sand or both by about 10% (by wt) would yield the optimum compressive strength, and that its replacement of cement by up to 30% would not reduce its compressive strength, significantly. It was found that OSA on its own possesses a limited cementitious value and that its contribution to mortar or concrete comes through its involvement in the pozzolanic reactions. The statistical model developed showed an excellent predictability of the compressive strength for mortar and concrete mixes.