Macro-defect-free Cement Research Articles

Improvement in hygroscopic property of macro-defect free cement modified with hypromellose/potassium methyl siliconate copolymer and pulverized fly ash

Improvement in hygroscopic property of macro-defect free cement modified with hypromellose/potassium methyl siliconate copolymer and pulverized fly ash

Polymer-Cement Composites Glazing by Concentrated Solar Energy

Macro defect free (MDF) cements are polymer-cement composites characterized by high biaxial flexural strength compared to traditional concrete, having as a drawback a low water resistance. Glazing these composite materials with an inorganic enamel containing TiO2 nano-particles has led to a high water-stable material with advanced photocatalytic properties. Classic glazing by thermal treatment of samples, at 1050 °C, requires energy consumption and long-time performing. The purpose of this paper is to test the use of solar radiation as a source of energy in the glazing process. A vertical axis solar furnace has been used, from PROMES-CNRS Solar Laboratory, Font-Romeu Odeillo, France, and it has been observed that a uniform appearance of the glaze coating has been achieved; it shows high scratch resistance, meaning a good hardness and adhesion to the substrate. The obtained film was also characterized by SEM, EDS and XRD, aiming to evidence the coat morphology, the TiO2 distribution and its crystallinity alteration, when compared to the samples obtained by classic thermal treatment. The conclusion of the paper is that using solar radiation in the MDF cement glazing process is a promising approach for obtaining multifunctional materials.

The effect of carbon nanotubes on the mechanical and damping properties of macro-defect-free cements

Abstract The effect of CNTs on the mechanical and damping properties of macro-defect-free (MDF) cements was studied, and polyvinyl alcohol (PVA) fibers were also studied as a contrast. It was found that the compressive strength of MDF cements was not significantly affected by the two types of fibers. The CNTs enhanced the flexural strength of MDF, while PVA fibers made negative contribution. The strengthening mechanism of flexural strength of MDF cements by CNTs can be summarized as fiber bridging, crack deflection and fiber slippage. For the damping properties, the proper contents of CNTs and PVA fibers improved the loss factor significantly. The interface transition zone (ITZ) between the PVA fibers and matrix was large, which was favorable for fiber slippage. The damping property of MDF cements with CNTs was mainly due to the slippage between the inner tubes of the CNTs rather than the slippage between the CNTs and matrix.

Tailoring the Properties of Calcium Aluminate Macro-Defect-Free Cements: From Brittle to Ductile Behavior

Cementitious macro-defect-free (MDF) materials can be obtained processing a mixture of a water-soluble polymer, namely polyvinyl alcohol (PVA) and the calcium aluminate cement. Based on process techniques typical of plastics, the MDF products can be obtained in complex forms and, thanks to the reduced water to cement ratio, w/c, their strength is very high compared to standard cements. However, these materials show both the sensitivity typical of water-soluble polymers, presenting a low glass transition temperature (Tg), and the brittle behavior typical of ceramic materials and therefore low toughness. The aim of this work is to modify the mechanical properties of MDF cements by tuning their unacceptable brittle behavior. Water solution of carboxylate styrene butadiene rubber is used as reactive additives, and different mixture formulations are tested changing the rubber-like content both with respect to the fixed water content and PVA amounts. It is shown that the modifications of the organic phase imply small or negligible effects on paste formation of different recipes as detected by the torque–time responses. From flexural and fracture toughness tests, a wide range of responses was observed, and depending on the particular recipe, the mechanical behavior can be tuned from a brittle to a ductile behavior.

Photoactive polymer-cement composites for tannins removal from wastewaters

The TiO2 nanoparticles exhibit a remarkable photocatalytic activity against wastewater organic pollutants but their separation from the liquid media after the photocatalytic process is a very difficult task. The immobilization of TiO2 on different supports could be a good solution to simplify the cleaning stage after photocatalysis. In this study, two types of photoactive polymer-cement composites named macro-defect free cements (MDF) were obtained both by embedding TiO2 nanoparticles (Degussa P25) in the composite matrix and by photocatalyst deposition on the composites surface through the dip-coating method (in two types of recipe). The composites surface was characterized by SEM and XRD and photocatalytic efficiency was determined against wastewater tannins from woodworking industry. The tannin concentration was monitored by VIS-spectrophotometry, using the Folin-Ciocalteu method. All specimens evidenced photocatalytic activity. The process efficiency is dependent on the light wavelength and on the irradiation duration. The best results were obtained when the MDF containing embedded TiO2 nanoparticles were exposed to 254 nm light (92% after 6 h). Under higher wavelength light irradiation (365 nm), the photocatalytic efficiency decreased to 48.2% for the MDF containing embedded TiO2 and to 39.85% for the MDF coated with a TiO2 film. The obtained results are promising both in terms of environmental protection, considering the persistence of tannins in wastewaters and the difficulties of their removal through the classic methods, and in terms of MDF property improvement, considering its potentially very large range of applications.

Photoactive glazed polymer-cement composite

Macro defect free cements (MDF), a kind of polymer-cement composites, are characterized by remarkably high mechanical properties. Their flexural strengths are 20–30 times higher than those of conventional cement pastes, nearly equal to that of an ordinary steel. The main drawback of MDF cements is their sensitivity to water. This paper presents a method to both diminish the negative impact of water on MDF cements mechanical properties and to enlarge their application by conferring photoactivity. These tasks were solved by glazing MDF cement with an ecological glaze containing nano-particles of TiO2. Efficiency of photocatalytic activity of this material was tested against methylene blue aqueous solution (4.4mg/L). Influence of the photocatalyst concentration in the glaze paste and of the contact time on the photocatalysis process (efficiency and kinetic) was studied. The best obtained photocatalysis yield was of 97.35%, after 8h of exposure to 254nm UV radiation when used an MDF glazed with 10% TiO2 in the enamel paste. Surface of glazed material was characterized by optic microscopy, scratch test, SEM, XRD, and EDS. All these properties were correlated with the aesthetic aspect of the glazed surface aiming to propose using of this material for sustainable construction development.

Microstructure–toughness relationships in calcium aluminate cement–polymer composites using instrumented scratch testing

We investigate the influence of the microstructure on the fracture properties of calcium aluminate cement/polymer composites. We carry out microscopic scratch tests during which a Rockwell C diamond probe pushes across the surface of a polished specimen under a linearly increasing vertical force. We extend the scratch fracture method to heterogeneous materials. The scratch test induces a ductile-to-brittle transition as the penetration depth increases. Scanning electron microscopy imaging shows that the low porosity and the strong cement-binder interphase favor toughening mechanisms such as crack trapping and bridging. Nonlinear fracture mechanics theory yields the fracture toughness in the fracture-driven regime. The fracture toughness of macro-defect-free (MDF) cement is found to decrease as the polymer-to-cement ratio increases. This decrease in the fracture resistance can be explained by the decrease in anhydrous cement content and the increase in the inter-particle distance between cement grains. By evaluating the fracture toughness of the micro-constituents of MDF cement, we show that the high value of the fracture toughness at the composite level stems from tough calcium aluminate phases and a highly packed non-porous granular microstructure.

MACRO DEFECT FREE CEMENTS: A REVIEW

The usage of polymers in different sectors has been increasing in recent decades, and even our current age may have been defined as polymer age. When concrete is considered polymers are also widely used to modify the properties of both mortar and concrete and the usage of polymers in concrete dates back to 1920’s. On the other hand, Macro-defect free (MDF) cements are one particular type of cement-polymer composites and developed and patented by scientists at Imperial College at the beginnings of 1980’s. MDF cements are produced by mixing cement (commonly calcium aluminate cement) with small amounts of polymer (usually polyvinyl alcohol acetate) and water. High shear, relatively low pressure (about 5 MPa) and moderate temperature (about 80-100 °C) are applied during the production of this material. MDF cements, although consist of more than 80% by weight of cement, show 20-30 times higher flexural strength comparing to ordinary Portland cements. However, MDF cements show a considerable reduction in strength when they are exposed to water even for a short time. Many studies have been conducted to solve the water sensitivity of MDF cements for over 30 years. In this study, production, basic properties and the current state of the art of MDF cements are explained, and the future research works are suggested.

Optimization of material characteristics of macro-defect free cement

Macro-defect free (MDF) cement is a high-strength cement–polymer composite produced by mixing cement (commonly calcium aluminate cement) with small amounts of polymer (commonly polyvinyl alcohol acetate) and water, applying high shear, and finally applying relatively low pressure (about 5 MPa) and modest temperature (about 80–100 °C). However, MDF cements lose considerable strength when exposed to water. The objective of this study was to explore the effects of cement and polymer compositions on flexural strength and water sensitivity. Calcium aluminate cements were used with Al2O3 contents between 42% and 79%. Production of MDF cement was successful with all cements, but the highest strength (268 MPa) was obtained with 70% Al2O3 cement. Secondly, PVAs were used that differed in their degree of hydrolysis between 73% and 99%. Of these, the one with a moderate degree of hydrolysis produced the highest strength (228 MPa). All mixtures had strength loss on exposure to water, but PVAs with moderate degrees of hydrolysis exhibited the lowest strength losses (50–60%).

Effect of Epoxy Resin Addition on the Moisture Sensitivity of Macro Defect Free Polymer-Cement Composites

Macro-defect-free (MDF) cements are cement-polymer composites and were developed by Birchall et al. three decades ago. The composites are produced by mixing small amounts of polymer and water with cement. However, they have a different production method than that of cement pastes, which was inspired by rubber production. Mixtures of cement, polymer and water are processed by using a two-roll mill. The composites are known with their high flexural strengths. Unfortunately, there are not any known commercial products using MDF cements because of their poor durability under moisture. In this study, MDF cements were prepared by using poly(vinyl alcohol--vinyl acetate) PVA, calcium aluminate cements and two different types of epoxy resins. Epoxy resins were a diglycidyl ether of bisphenol A and a mixture of a diglycidyl ethers of bisphenol A and F. Durability performance was compared with respect to biaxial flexural strengths, contact angle and atomic force microscopy (AFM) for the specimens stored in water.

Influence of the obtaining technology on the Macro Defect Free cements characteristics

Macro Defect Free (MDF) cements are cement polymer composites obtained by using water soluble polymers aiming to achieve very high mechanical properties. In spite of their excellent flexural strength, the main issue of these composites is the behavior in humid atmosphere. MDF flexural strength decreases sometimes more than half of their initial strength when the samples are in contact with water. Aiming to improve the water sensitivity of MDF samples, new methods have been proposed. The effects of obtaining technology of MDF on their characteristics from morphological point of view, by using contact angle measurements have been studied.

Macro-defect-free (MDF) cements

MDF cements using the blends of sulfoaluminate ferrite belite (SAFB) clinkers and ordinary Portland cement (OPC) in mass ratio 85:15 with Al2O3, and starch, polyphosphate (poly-P) or butylacrylate/acrylonitrile were subjected to moist atmospheres (ambient, 52 and 100% relative humidity (RH)) to investigate their moisture resistance. Their chemical, thermal, electron microscopic and magnetic properties were also studied before and after moisture attack. Butylacrylate/acrylonitrile (BA/AN) copolymer was found to be the most suitable for MDF cement synthesis since the sample containing BA/AN showed the best moisture resistant. There are significant differences in scanning electron microscopy (SEM) of MDF cements before and after moisture attack and with different polymers. New data on the paramagnetic nonhysteresis magnetization curves for all the samples are observed. The MDF cements synthesized from SAFB clinker with dissolved poly-P give the best signal/noise (S/N) ratio. Three main temperature regions on TG curves of both series of MDF cements are observed. In the inter-phase section of MDF cements, the content of classical cement hydrates decomposing by 250°C is increased. Combustion of organic material took place by 550°C. In the temperature range 550-800°C, the decomposition of CaCO3 occurs.

Synthesis, moisture resistance, thermal, chemical and SEM analysis of macro-defect-free (MDF) cements

The results, presented here discusses the Macro-Defect-Free (MDF) cements prepared from the blends of sulfoaluminate ferrite belite (SAFB) clinkers, ordinary Portland cement (OPC), Al2O3 and poly(butyl acrylate) (PBA), styrene/acrylonitrile co-polymer (SACP) or sodium polyphosphate (poly-P). Though MDF cements have several attractive properties, their utilization has been limited due to the insufficient moisture resistance. It is a very challenging task for scientists and technologist to improve the moisture resistance of MDF cements. Therefore, the new MDF cements were subjected to various moist atmospheres to investigate their moisture resistance. The most significance of this work is the improvement of moisture resistance of the studied MDF cements. The aim of this work was to understand the effects of polymers, Al2O3, OPC and SAFB clinkers in the raw mix and delayed drying on MDF cements and also on their subsequent moisture resistance and thermal stability as well as to discover the new properties of these materials. Their chemical, thermal and scanning electron microscopic (SEM) analysis was also carried out before and after exposure to moisture. PBA was found to be the most suitable polymer for MDF cement synthesis, since the samples containing PBA showed the highest resistance to moisture. There are three main temperature regions on TG curves of both series of MDF cement samples. The significant differences in SEM of MDF cements before and after moisture attack and with different polymers were observed.

Macrodefect-Free Cements: Chemistry and Impact of the Environment

Macrodefect-Free Cements: Chemistry and Impact of the Environment

Influence of organic coatings on the stability of macrodefect-free cements exposed to water

It is known that macrodefect-free (MDF) cements show instability in water, with swelling and reduction in strength. The weight and dimensional changes of three MDF cements, formulated from different aluminous cements, during immersion in quiescent tap water, were evaluated. The results show that the cement with the highest Al 2O 3 percentage had the lowest degradation after prolonged immersion. Hence, this material was selected for further analysis. As the time taken for water to diffuse into the body of MDF composites is considered a key factor in the collapse of their mechanical properties, the effect of organic coatings with different barrier properties on the composite behaviour, when exposed to water, was studied. The water permeability of seven surface coatings was evaluated by electrochemical impedance spectroscopy (EIS). Three of them were chosen for application to the selected MDF cement. The data presented show that the application of organic coatings, not necessarily characterised by extremely low water permeabilities, improves the stability of the composite when subjected to different conditions of exposure to water.

Changes of thermal events of macrodefect-free (MDF) cements due to the deterioration in the moist atmosphere

Sulfoaluminate ferrite belite (SAFB) clinker premixed with Portland cement in mass ratio 85:15 was combined with hydroxypropylmethyl cellulose (HPMC) or sodium poly-phosphate (poly-P) for the macrodefect-free (MDF) process and subsequent moisture treatment. Mass changes as the measure of the moisture resistance and thermoanalytical traces of MDF cements gave useful information. The mass change depends more on the humidity than on the composition (polymer and inorganic constituents) of the MDF cement or duration of the original MDF cement synthesis. The values of mass changes at 100% relative humidity (RH) and at ambient conditions are affected by the nature of the polymer, poly-P being highly advantageous. Attack by environmental water and carbon dioxide increases the contents of C 4( A, F) S̄H 12( AFm) and CaCO 3, represented by thermogravimetry (TG) effects at 250°C and differential thermal analysis (DTA) peaks at 600–700°, respectively. In contrast, the quantity of cross-linking, where the decomposition of Al(Fe)–O–C(P) bonds typically produces TG–DTA effects at 250–550°C, remains intact during the moisture attack.

建設材料 ホットプレス成形によるＭＤＦセメント硬化体の耐水性改善

In general, MDF (macrodefect-free) cements are produced by using portland cements and water-soluble polymers, and applying mechanochemical processing techniques at very low water-cement ratios, and have flexural strengths of 50 to 70MPa under dry conditions. However, MDF cements have a poor water resistance because of the nature of the water-soluble polymers used, therefore, the precast products made of MDF cements have not been commercialized in the world. MDF cements using a portland cement, a water-soluble polyacrylamide, an epoxy resin and a phenol resin are prepared with various mix proportions by applying a kneader mixing process, hot press molding process and heat cure, and tested for water resistance through a change in flexural strength and water absorption during water immersion. The effects of the mix proportions for the hot press molding process on the water resistance of MDF cements are examined to find out the effective processing techniques for improving their water resistance. As a result, the water resistance of MDF cements is markedly improved by applying the hot press molding process and heat cure to them with the optimum mix proportions, i.e., a polyacrylamide content of 6.0%, an epoxy resin content of 6.0%, a phenol resin content of 2.0% and a water-cement ratio of 8.0%. The application of the hot press molding process to MDF cements is considered to be effective for the simplification of their manufacturing process.

A preliminary investigation of glass polyalkenoate cements based on waste gasifier slags

Glass polyalkenoate cements (GPC) used for dental and biomedical applications, are formed by reacting aqueous poly(acrylic acid) (PAA) with specially synthesized calcium aluminosilicate glasses, generally containing fluoride [1]. The acid degrades part of the glass network releasing metal cations, typically Ca2+ and Al3+. The cations subsequently serve to form salt bridges between the polyacid chains and result in the formation of a hard cement [2]. The setting reaction is shown schematically in Fig. 1. One of the most important properties of the glass component is its susceptibility to acid attack . This is determined by the number of hydrolyzable bonds present in the glass network and in particular the silicon to aluminum ratio. The glass can be thought of as consisting of linked [SiO4] tetrahedra and [AlO4] tetrahedra. Since an Si4+ ion is being replaced by an Al3+ ion, the network will acquire a negative charge. This is balanced by a positive charge of a network dwelling cation, for example Ca2+. It has been found that to obtain four coordinate aluminum, the calcium to aluminum ratio must be greater or equal to than 1 : 2 and the silicon to aluminum ratio must be greater than 1 : 1. The oxygen linkage between adjacent aluminum and silicon tetrahedra is vulnerable to acid attack. The difference in electronegativity between the Al3+ ion and that of the Si4+ ion results in a sufficient residual polarizability of the aluminum oxygen silicon bond to be susceptible to acid attack. The degradation mechanism of the glass network by acid is shown schematically in Fig. 2. Wilson et al. [3] and Hill et al. [4] have reviewed a wide range of simple calcium aluminosilicate glasses and related the chemical compositions to their acid degradability and the mechanical properties of the resulting polyalkenoate cements. These studies provided strong evidence that the aluminum to silicon ratio is a dominant factor determining cement properties in simple CaO-Al2O3-SiO2 glasses. Hill et al. [4] specified a Si : Al close to one, a Ca : Al ratio of 1 : 2 and a silica mole fraction of less than 0.6 for glass polyalkenaote cement formation. Rodgers et al. [5] highlighted the similarity between glass polyalkenoate cements (GPC) with “macro defect free cements” based on polyacrylamide. Hydroxyl ions present from the lime in ordinary portland cement (OPC) catalyze the partial hydrolysis of the amide functional groups in the polyacrylamide, giving rise to car-

Applications of High-Performance Fiber-Reinforced Cement-Based Composites

Advanced composites and the fundamental understanding of their behaviour is a rapidly expanding branch within the field of civil engineering materials. In particular, fiber-reinforced cement-based materials have had a great evolution in these years, so that they are more and more utilized in the building sector. Besides, large efforts have been made to develop high-performance cements and concretes showing further performance improvements. High-performance fiber-reinforced cement composites include, for example, materials such as SIFCON (Slurry Infiltrated Fiber CONcrete), fiber-reinforced DSP (Densified with Small Particles), and fiber-reinforced MDF (Macro-Defect-Free) cements. Developments of these materials were possible due to: (a) the introduction of new reinforcement systems; (b) the development of high-performance cement-based matrices, which present greatly improved microstructural properties in terms of strength and durability; (c) the development of adequate processing techniques (including controlling chemical reactions) which allow us to obtain composite materials with surprising toughness properties. After a brief description of high-performance cement-based matrices and relative composites, two different examples among the above-cited products will be deeply presented.

Macro-defect free cements Influence of poly(vinyl alcohol), cement type, and silica fume

Macro-defect free cements were prepared using the following variables: processing (calendering and hand-mixing), poly(vinyl) alcohol (with different molecular weight and hydrolysis degree), cement (portland type I and slag-modified), and additions of silica fume. The results show that better processing is achieved by calendering the fresh paste and using poly(vinyl alcohol) with low hydrolysis degree and low molecular weight. Vickers hardness measurements indicate that materials prepared using portland type I cement are not significantly affected by humidity. Addition of silica fume lowers the acid resistance of these materials, suggesting that silica fume acts as an inert filler.