Physical and mechanical properties of durable sisal fiber–cement composites

Sisal fiber–cement composites reinforced with long unidirectional aligned fibers were developed and their physical–mechanical behavior was characterized in the present study. Flat and corrugated sheets were cast by a manual lay-out of the fibers in a self-compacted cement matrix and compressed with a pressure of 3 MPa. Direct tensile and bending tests were performed to determine the first crack, post-peak strength and toughness of the composites. Drying shrinkage, capillary water absorption and water tightness tests were performed to characterize the physical properties of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin and calcined waste crushed clay brick to consume the calcium hydroxide generated during Portland cement hydration. The durability of the newly developed composite was determined through accelerated aging conditions using the hot-water immersion test. The developed material presented a multiple cracking behavior under bending, even when subjected to 6 months of hot-water immersion under 60 °C. Scanning Electron Microscopy was used to investigate the micro-structure of the composites before and after aging.     

Dynamic testing of a soil–steel composite railway bridge

Actual dynamic response of a long-span corrugated steel culvert railway bridge is studied. The bridge, which is a type of soil–steel composite structures, has a span of 11 m. Tests were carried out by measuring strains and displacements during passages of a locomotive at different speeds. Vertical ballast accelerations as well as the effects of braking forces were also measured. The tests showed that the speed has a large influence on the displacements, thrusts and moments. The measured dynamic displacements and thrusts are as much as 20% larger than the corresponding static response. This is greater than the values specified in bridge design codes. Dynamic amplification factors as high as 1.45 were obtained for the moments at the quarter point which is found to be much larger than the values for the crown point. This type of bridge structure is believed to be less sensitive to resonance from passing trains than other common bridge types, due to the high damping values obtained from the forced vibration tests.     

Carbon nanotube–cement composites: A retrospect

Although ordinary Portland cement (OPC) is widely used in the construction industry, its weak tensile strength, to some extent, limits its application. A carbon nanotube (CNT), on the other hand, has outstanding mechanical properties with a tensile strength of 63 GPa and Young's modulus of 1 TPa, making it a candidate as nano-scale reinforcements in OPC. Past research studies have reported improved mechanical and electrical properties of carbonnanotube–ordinary Portland cement (CNT–OPC) composites, which show future promise in practical civilengineering applications. In this study, recent research studies in developing CNT–OPC composites are comprehensively reviewed. Highlighted herein are the considerable efforts been made in the study of fabrication, hydration, porosity and transport properties of the CNT–OPC composites. There are, however, future investigations needed to provide a better understanding in the areas of uniform dispersion of CNTs within the OPC paste, durability, impact, fatigue properties and the theoretical modelling of CNT–OPC interaction.     

Comparing flexural behaviour of fibre–cement composites reinforced bagasse: Wheat and eucalyptus

In this paper the applications of Agricultural Waste Fibres (AWF) are considered in producing the Fibre Cement Boards (FCB). Three different AWFs including bagasse, wheat and eucalyptus fibres as 2% and 4% by the weight of Portland cement, were used to produce FCB. Moreover, the effect of silica fume on flexural behaviour characteristics of FCB has been studied. The results show that the flexural behaviour of the FCBs depends on the type, length, diameter, aspect ratio and texture of fibres. Also for all groups with increasing fibre content from 2% to 4% of cement weight, maximum flexural strength increases. Moreover, silica fume could improve the flexural strength for all the groups.     

Thermal characteristics of high-strength polymer–cement composites with lightweight aggregates and polypropylene fiber

Recently, research has been conducted using fibers to reduce the explosive spalling of concrete. Assessments of the volume fraction of polypropylene fiber in high-strength and lightweight concrete has shown that an optimum volume fraction of fiber reduces explosive spalling by discharging pore pressure and heat stress inside the concrete through the dissolution of fibers during exposure to high temperatures. In this study, we manufactured a high-strength polymer–cement mortar that can be used in repairs of many concrete structures by selecting three kinds of lightweight aggregate that have excellent heat interception performance, combined with varying volume fractions of polypropylene fiber to reduce explosive spalling. We analyzed the thermal characteristics and physical and mechanical properties of the mortar at high temperature. The analysis of test results for compressive strength, flexural strength, thermal conductivity, and thermogravimetric showed that a mixture of expanded perlite with high thermal stability and 0.2% polypropylene fiber showed the best physical, mechanical, and thermal characteristics.     

Effects of fineness of cement on polynaphthalene sulfonate based superplasticizer–cement interaction

The effects of fineness of portland cement procured from six different Turkish cement plants, on superplasticizer/cement interaction were investigated. CEM I 42.5 type portland cements (PC) were ground into different finenesses ranging from 280 to 550 m²/kg Blaine values. The effects of PC fineness on initial fluidity and fluidity loss of superplasticized cement paste were evaluated. It was found that increasing the Blaine fineness of incompatible cement up to a certain level reduced the viscosity of cement pastes but had no marked effect on the yield stress of the paste mixtures. Nevertheless, flow loss and also saturation point at 60 min increased with increasing the cement fineness. In other words, pastes with lower viscosity can be produced by using finer cement and more superplasticizer.     

Development of calcium sulfate–ggbs–Portland cement binders

Binders manufactured using a blend of gypsum, ground granulated blast furnace slag and Portland cements are technically viable and possess considerable environmental and economic advantages when compared to binders manufactured using Portland cement alone. As such, the evaluation of binders made from these materials offers a promising research focus in the quest to produce technically sound, environmental and economical binders for specialist uses as an alternative to traditional concrete binders of higher carbon footprint. The aim of the test programme was to investigate the viability of a series of binders designed to fulfil particular user needs while having significantly decreased carbon footprints.Two distinct series of binders were designed; the dominant ingredient in the first was calcium sulfate while in the second it was ggbs. Potential applications for both series of binders were considered and the strength development of each binder was analysed. In addition, the effect of water on the gypsum-based binders was analysed, as was the sulfate resistance of the ggbs-based binder.The results of the laboratory tests carried out were varied. For the calcium sulfate-based binders, those manufactured using anhydrite II as the dominant ingredient were found to achieve highest strengths. However these binders were found to be particularly susceptible to moisture-induced deterioration. For the ggbs-based binders, it was found that the early strength development was improved by the addition of small quantities of anhydrite II and gypsum. The strengths and sulfate resistance at later ages remained unaffected. These binders may have significant potential in situations where early strength development is a requirement.     

Geotechnical characterization of a clay–cement mix

Soft clay deposits are highly plastic, normally consolidated fine grained soils characterized by their low inherent shear strength. The mixing of soft clays with cement as a chemical stabilizer has become a well-known stabilization technique. The resulting strength of the clay–cement mix is controlled by different factors, but mainly the water to cement ratio, the cement content, and the curing conditions. It is crucial to develop a clear understanding of the changes in engineering behavior of the clay–cement mix that result from changes in controlling factors. A phase diagram was established to define the initial conditions of the mass–volume relationships of air, cement, clay, and water of a typical clay–cement mix. This phase diagram was then used to determine the total dry density, void ratio, and specific gravity of the clay–cement mix as a function of the cement content and water to cement ratio. The main objective of this work was to develop generalized trends for the geotechnical properties of clay–cement mixes. These trends were evaluated based on unconfined compressive strength as well as consistency tests carried out on soft clay samples before and after mixing with cement and at different curing times. A reduction in the plasticity index (PI) of 16 % and an increase in the unconfined shear strength of more than 200 kPa were obtained from the addition of 15 % cement. The reduction in the PI of the clay–cement mix was found to be an efficient tool to represent the improvement in the strength of the clay after mixing with cement.     

Hydration of coal–biomass fly ash cement

This paper presents possibilities of use of fly ashes from co-combustion bituminous coal and biomass in cement production process. Both fly ashes coming from co-combustion bituminous coal and biomass and the ones from bituminous coal combustion were analysed. The following properties of cement were tested: heat of hydration, Ca(OH)₂ content, unreacted C₃S content and microstructure. The results showed that fly ashes from co-combustion coal and biomass retard cement hydration. Cement samples containing coal-biomass fly ashes demonstrate adverse features like lower heat of hydration, higher Ca(OH)₂ content and lower rate of C₃S hydration in comparison to the ones containing fly ashes from bituminous coal. The incorporation of coal-biomass fly ashes in cement results in an increase of porosity of cement paste, leading to a microstructure of lower density.     

Composition and reaction mechanism of cement–asphalt mastic

In order to improve the performance of asphalt concrete under heavy traffic, cement as reinforcement is used to mix with emulsified asphalt in asphalt mastic. But cement and emulsified asphalt is hard to mix well. Thus, F-type superplasticizer (FSP) as the isolation layer outside the micelles in cationic emulsified asphalt (CEA) is used in cement asphalt mastic (CAM). Emulsified asphalt and cement can mix effectively without the generation of any viscosity by demulsification. Sodium carboxymethylcellulose (CMC-Na) is added to improve and restrain settlement and stratification of the mixed mastic. This study is to investigate the effects and reaction mechanisms associated with mixing FSP and CMC-Na into cement–asphalt mastic.     

Effects of water–cement ratio and curing time on the critical pore width of hardened cement paste

Mercury intrusion porosimetry (MIP) test is one of the techniques that have been widely used for analyzing the pore size distribution of hardened cement paste (hcp) and also for the determination of the critical pore width. This study presents the test results of the MIP experiments obtained for three different hcp specimens with the water–cement ratios of 0.26, 0.34, and 0.42 which had been cured for 7, 28, and 365 days under water. Thus, the effects of water–cement ratio and curing time on the critical pore width of hcp were investigated. Test results have shown that, within the limits of the work, and in case of complete hydration, the critical pore width of the hcp seems to be independent of water–cement ratio and is of the order of 25 nm. This value can be considered as the critical pore width of the portland cement gel.     

Optimization of fineness to maximize the strength activity of high-calcium ground fly ash – Portland cement composites

Depending on their physical and chemical properties and the amount of replacements with cement, fly ashes may provide an economical production possibility in concrete industry and improve the mechanical and durability performance of concrete. In recent years, ultrafine fly ash has become one of the necessary ingredients of high-performance concrete. However, many of the fly ashes are coarse in nature, hence grinding is necessary to obtain sufficient performance in concrete production. In this study, the effect of grinding on strength activity of ground high-calcium fly ashes was investigated. Physical characteristics such as sieve fineness, grain particle size characteristics and Blaine specific surface area were also determined and compared with raw fly ash. Some case studies and possible interactions between fineness of fly ash, strength and water demand of mortars were discussed. The optimization of fineness coupled with the adjustment of water content were found as the key parameters of effective utilization of high-calcium fly ashes from the view point of strength maximization of cement mortars.     

Chemical–physical behaviour of matt waste in cement mixtures

The chemical and physical behaviour of matt waste (MW), a by-product which derives from purification processes of cullet from separated glass waste collection, has been studied as new component for cement based materials. Up to now, recycling for MW is not fully exploited. The aim of this research is to investigate the possible benefits of MW addition to cement systems. Investigations on paste samples cured in accelerated conditions were carried out with different analytical techniques (FT-IR, TGA, SEM, MIP) to investigate MW reactivity with portlandite and its effect on pastes microstructure. The results highlight pozzolan behaviour of MW at long curing time and a refinement of porosity leading to a compact microstructure.     

Effect of sepiolite on retention and drainage of suspensions of fiber–reinforced cement

This research is focused on the study of the effect of rheological grade sepiolite on flocculation, retention and drainage of fiber–cement suspensions by using a focused beam reflectance measurement probe and a vacuum drainage tester. Results show that the sepiolite could be used in the manufacture of fiber–cement to increase the retention of solids and the drainage rate especially in mixtures containing poly(vinylalcohol) fibers.     

The influence of moisture on the deformability of cement–polymer adhesive mortar

Adhesive mortars are widely used to set porcelain stoneware tiles on buildings because their bond strength and flexibility properties increase the cladding serviceability. However, their long-term performance is not well understood, mainly the degradation of the polymeric matrix.The influence of moisture content on the flexibility of six adhesive mortars is investigated, based on standard EN 12002. Four of them have defined formulations and the other two are commercial and are widely used to set porcelain stoneware tiles on building façades in Brazil.The results show that moisture content above 6% is sufficient to reduce 50% of the mortar deformability, but that the drying process allows it to recover to a value similar to that prior to saturation; a logarithmic function best fits the correlation between moisture content and flexibility; water immersion increases matrix rigidity.It is suggested that standards should consider flexibility tests on both dried and wet samples as a requirement for polymer-modified mortars.     

Development of cork–gypsum composites for building applications

This paper presents an experimental analysis on a new composite material, cork–gypsum composite. It is shown that cork and plaster are mutually compatible and that a lot of new building materials can be made by mixing those materials in different volume fractions. Mechanical properties of the cork–gypsum composite have been measured. The acoustic absorption coefficient and thermal conductivity of this new composite have also been experimentally obtained and those values are reported for design purposes. Concerning the acoustical insulation characteristics, this composite is not a sound-absorbing material but a reflecting one, and it needs some kind of perforations to behave as an absorbing construction material for sound and noise. The thermal insulation properties are quite good as a result of the thermal conductivity tests. This new composite material is suggested for use in building applications as partitions.     

Recycling of the product of thermal inertization of cement–asbestos for the production of concrete

A novel field of research in materials science is the recycling of secondary raw materials for construction and building materials such as concrete. This paper describes the successful recycling of as much as 20 wt% of the product of thermal transformation of cement–asbestos for the formulation of concrete. The main mineralogical phases present in the product of transformation of cement–asbestos are C2S, ferrite, and Al-, Ca-, Mg-rich silicates such as akermanite (ideally Ca₂MgSi₂O₇) and merwinite (ideally Ca₃Mg₂Si₂O₈). The behavior of this secondary raw material, termed KRY·AS, in commercial concrete was investigated using five different mixtures in which various portions (0, 5, 10, 15 and 20 wt%) of cement were substituted by KRY·AS. The results of preliminary technological tests (slump test, compressive strength, flexural strength after 28 days, and depth of penetration of water under pressure after 28 days) were discussed and interpreted with the aid of chemical, mineralogical and SEM analyses.One of the major results is that after 28 days, although all the concrete samples are invariably classified as “ordinary concrete” according to the UNI 6132 tests, those diluted with KRY·AS display a lower resistance to compression with respect to the standard. On the other hand, they recover compressive strength and display values identical to that of the standard after 90 days. The addition of the secondary raw material has the effect to slow down the kinetics of setting/hardening because the main cement phase present in KRY·AS is C2S which has a slower rate of hydration with respect to C3S.     

Hydration characteristics of hydrothermal treated cement kiln dust–sludge–silica fume pastes

Cement kiln dust (CKD)–sludge–silica fume pastes were hydrothermally hardened at a pressure of 8 atm of saturated steam for different autoclaving ages. Hydration characteristics of the autoclaved CKD–sludge–silica fume pastes were studied by the determination of compressive strength and chemically combined water contents at different autoclaving ages. The phase composition and morphology of the formed hydrates were studied using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The replacement of silica fume in CKD–sludge mixtures results in a marked increase in strength values of the autoclaved specimens at all stages of the hydrothermal process. The results of X-ray diffraction analysis and SEM-micrographs of autoclaved specimens for various mixtures indicates that the main hydration products identified are calcium silicate hydrates and minor amounts of CaCO₃.     

Low-temperature tensile behaviour of asphalt binders: Application of loading time–temperature–conditioning time superposition principle

Thermal cracking of bituminous layers is one of the main modes of failure for asphalt pavements. This distress is highly related to the rheological properties of asphalt binders. The purpose of this study was to investigate the low-temperature behaviour of asphalt binders by performing Direct Tension Tests (DTTs) according to Superpave specification. The DTT results were analyzed and compared in terms of trend of stress–strain curve instead of conventional failure stress or failure strain values. Through the analysis of stress–strain diagram, it was possible to evaluate the effects of temperature, elongation rate and conditioning time on the rheological properties of binders. Particular attention was paid to the conditioning time variable as it was observed that the stiffness of the binder changes with time when it is stored isothermally at low temperature due to the physical hardening phenomenon.To this end, a modified superposition effects principle, which also includes the conditioning time in addition to the temperature and elongation rate variable, has been proposed. Finally, this principle allowed the authors to find an analytical model capable of describing the rheological properties of asphalt binders as functions of the three considered test variables.