Macro-defect-free Research Articles

Enhancement of strength and water resistance of macro-defect free （MDF） gypsum modified by pregelatinized starch and hydrogen silicone oil

Gypsum, as a building material with renewable and environmentally friendly characteristics, is severely limited due to its poor mechanical properties and water resistance. Here, this paper investigates pregelatinized starch and hydrogen silicon oil modified macro-defect free (MDF) gypsum composite prepared by pressing. The compressive strength, water absorption, and softening coefficients of foamed MDF gypsum composite were subjected to strict testing. The hydration products, microtopography and pore structure was characterized using XRD, FTIR, SEM and LF-NMR. The result shows that the compressive strength of MDF gypsum composite with 5 % pregelatinized starch was 82.4 MPa, a 44.5% increase compared to the dry blank group, whilst water absorption also rose by 7.8%. Additionally, the compressive strength of MDF gypsum composite with 5 % pregelatinized starch and 1% hydrogen silicon oil was 123.9 MPa, 225.2% higher than that of the dry blank group. The water absorption rate decreases to less than 1.2%. Pregelatinized starch and hydrogen silicone oil assist in the accumulation and arrangement of crystals, while also reducing the space between them. The enhancement mechanism of compressive strength and water resistance of MDF gypsum involves pore filling by pregelatinized starch, as well as crystal contact point modification including stronger adhesion by the pregelatinized starch and hydrophobic properties of hydrogen silicon oil.

Enhancement and mechanism of macro-defect free (MDF) gypsum water resistance achieved by hydrophobic modification

Macro-defect free (MDF) gypsum is characterized by high strength and has the potential designed to advanced functionalization materials. However, the application of MDF gypsum is still limited by its poor water resistance. Here, we propose to modify the gypsum surface to hydrophobicity at molecule scale by adding potassium methylsilicate. The compressive strength, softening coefficients, and water absorption were subjected to rigorous testing, while elucidating the underlying mechanisms of water resistance enhancement through micro-structural analysis and organic-inorganic interactions. The results show that when adding 0.25% potassium methylsilicate, the wet compressive strength, softening coefficients are increased by 30.1%, 28%, respectively. And potassium methylsilicate can change the gypsum surface to hydrophobicity, which delaying the initial rapid water absorption stage and decrease both the 2 h and 24 h water absorption. The addition of potassium methylsilicate leads to a reduction in the dried compressive strength, attributed to the decrease in intrinsic dihydrate crystal strength. Upon the introduction of potassium methylsilicate, there is a transformation in gypsum crystal morphology from strip-like to lamellar structures. This alteration is accompanied by the formation of a potassium methylsilicate film coats the surface of gypsum, impeding water-gypsum contact. The potassium methylsilicate film coats on the surface of gypsum, which hinders the contact of water and gypsum.

Effect of sodium methylsilicate on mechanical and water resistance of macro defect-free (MDF) gypsum

Finding vicarious building materials for Portland cement and reducing the usage of cementitious materials is a key to reduce the carbon emission of cement production. Desulfurization (FGD) gypsum powder is a common solid waste which application is limited by its low mechanical strength and poor water resistance properties. This paper studies the effect of sodium methylsilicate on the mechanical performance and waterproofs of macro-defect free (MDF) gypsum involving pressurized processing. The compressive strength, flexural strength, water absorption rate, softening coefficient and water contact angle of the MDF gypsum are assessed. The results show that adding 1.6 wt% sodium methylsilicate achieves to the maximum strength of 7.5 MPa for flexural and 35.7 MPa for compressive, which increasing by 4.2% and 6.6% relative to the pure MDF gypsum, and increasing by 11.9 % and 138.0 % relative to traditional casting gypsum. With the increasing content of sodium methylsilicate, the waterproofs of MDF gypsum become better. When adding 1.6 wt% sodium methylsilicate, the water absorption rate, softening coefficient and water contact angle is 0.4 %, 0.78 and 93.5° for 2 h immersion, respectively. The pressurized production is recommended to prepare MDF gypsum.

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.

Polymer-Modified Calcium-Aluminate Macro Defect Free (MDF) Cements

Cementitious Macro Defect Free (MDF) materials can be obtained in complex forms with high performance making these materials suitable for applications in many sectors. The low water to cement ratio, w/c, and the saturation of voids by means of water soluble polymers allows increasing the cement strength. However, in their standard form 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 with various techniques the standard formulation of MDF materials by modulating toughness from a brittle to a ductile behavior. In addition, the effect of the recipes modifications will be analyzed by comparing the rheological characteristics along the processing stages.

State of the art of macro-defect-free composites

Macro-defect-free (MDF) composites, developed and patented by scientists from Imperial Chemical Industries in the early 1980s, are very high strength cement–polymer composites. The preparation of MDF composites is different from the production of conventional cement paste in that high shearing with a roller mill as well as moderate pressure (about 5 MPa) and moderate temperature (about 80–100 °C) are applied during the production. Very low water/cement ratio (w/c) levels are achieved (as low as 0.10) in this composite, much lower than in other cement-based materials. Of the many unique properties exhibited by MDF composites, surely the most remarkable is their high flexural strength. This is generally attributed to their low porosity and to cross-linking reactions between cement and polymer. MDF composites may reach a flexural strength of 200–300 MPa levels, whereas ordinary cement pastes have generally around 5–10 MPa. However, serious durability problems are observed in MDF composites, particularly their significant reductions in strength when immersed in water. Comprehensive information about MDF composite research will help in understanding the reasons behind the high strength, microstructure and water sensitivity of MDF composites. This review summarizes the materials, production methods, properties, microstructure, hydration reactions, durability and potential application areas of MDF composites as published since 1981.

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.

Effect of polyacrylic ester emulsion on mechanical properties of macro-defect free desulphurization gypsum plaster

This paper investigates the effect of polyacrylic ester emulsion (PEE) addition on the mechanical properties of macro-defect free (MDF) desulphurization gypsum plaster prepared through pressurized processing. The hydration kinetics, chemical composition and microstructure of the formed plasters are characterized by ICC, XRD, TGA, FTIR, BET and SEM. The result shows that 1wt% PEE addition leads to the maximum compressive strength of 46.9MPa in the plaster, which increases by 185.7% relative to the pure gypsum plaster, while 4wt% PEE addition leads to the maximum bending strength of 20MPa to increase by 23.4%. Although the PEE addition restricts the hydration of gypsum particles, the PEE particles also fill in the pore structure of the plaster to enhance its mechanical property. The MDF production through pressurized processing used for preparing the desulphurization gypsum plaster with high strength development is recommended.

The challenge of methods of thermal analysis in solid state and materials chemistry

Abstract Thermogravimetry (TG) and differential thermal analysis (DTA) are traditional, but still useful, experimental techniques for obtaining information in the realms of materials and solid state chemistry. This paper presents two case studies (many more could be cited) to illustrate the strengths (and limitations) of these techniques: (1) Iron doping of clinoptilolite (the most common zeolite): the typical parameters of both components appear clearly in the TG and DTA curves. The decrease of the Tmax value of the structurally-typical DTA effect of FeOOH by approximately 100°C is attributed to the weakening of chemical bonds in FeOOH due to the incorporation of the doping component into the structure of this zeolite. (2) Macrodefect-free (MDF) materials: the results of both TG and DTA unambiguously locate the typical temperature range of the decomposition of the P{4}–O–Al/Fe{6} cross-links within the interval of 200–300°C. The presence of cross-links is shown by the DTA data while the TG data can be used to measure the degree of cross-linking, which is valuable information when studying both raw mixes and the final materials for a variety of MDF materials.

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.

Utilization of XPS Analysis for the Characterization of Mechanochemical Activation in Polymer-Cement Composite Materials

This paper introduces the X-ray photoelectron spectroscopy (XPS) technique, well applicable for the analysis of the interfacial layer between polyvinyl alcohol and monocalcium aluminate in macro defect-free (MDF) cement. The experimental results explain the chemical reaction mechanism during the mechanochemical process, which is crucial for the formation of those non-traditional polymercement composite materials.

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.

ChemInform Abstract: Contribution of Materials Chemistry to the Knowledge of Macro‐defect‐free (MDF) Materials

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Contribution of materials chemistry to the knowledge of macro-defect-free (MDF) materials

The latest studies on the reactivity of inorganic-polymeric networks in selected cement-based materials and the focus toward nano- and atomic levels of grafting of polymers on interfaces represent some of the success stories of materials chemistry. Recent developments are reviewed and discussed, with particular emphasis on macro-defect-free (MDF) materials. Experimental evidence of next-nearest-neighbor (NNN) interactions has led to the definition of the scope and model of Al(Fe)–O–P cross-linking under mechanochemical synthesis conditions, in a system combining the most common (Portland) cement and commercially available polyphosphates. Current approaches to synthesis of MDF materials, together with the atomic-level interpretations of both the formed functional interfaces and the adverse influence of moisture, are discussed.

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.

Potential of Portland cements for MDF materials

Macro-defect-free (MDF) materials comprise a “hot topic” example in the field of cement-based materials and composites. The methods of MAS-NMR and thermal analysis gave key data for monitoring the scope of Al–O–P cross-links both in virgin MDF test pieces and in those exposed to moisture. The increased contents of calcium aluminate hydrates, calcium silicate hydrates and CaCO 3 in moisture-attacked (as opposed to virgin) MDF probes have been detected by these methods. The controlling feedback from cross-links and interfaces to the extent of secondary interactions of MDF materials with out-door atmospheric humidity is evident. Data on both the next-nearest-neighbour (NNN) interactions and the thermal stability of cross-linked interfaces show that for MDF materials chemical knowledge is crucial to (i) procedure design; Al–O–P cross-linking is the key nano-scale aspect of the MDF formation process and (ii) exploitation; interfaces comprise compact and stable regions in which Al–O–P cross-links support moisture resistance in the MDF materials.

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.