The key to the processing and properties of Macro-Defect Free (MDF) cement composites is the interaction between the cement and the polymer. In calcium aluminate (CA) / polyvinyl alcohol (PVA) MDF composites, it has been hypothesized that aluminate (Al(OH)4−) ions released from the cement cross-link PVA in a manner similar to the well known interaction of the borate (B(OH)4−) ions with PVA. In this investigation, stable aluminate/PVA solutions at different concentrations have been studied. Results indicate that the nature of interaction of aluminate ions is not similar to that of borate ions in dilute and semidilute polymer solutions.

Relationships between mixing conditions, viscoelastic paste properties and flexural strength of hardened matrices have been investigated for an MDF cement. The correlation of paste relaxation times and matrix mechanical properties with mixing intensity suggests the build up and eventual breakdown of a network structure during mixing.

This paper describes the synthesis, structure and properties of a new layered nanocomposite which may have applications in cementitious systems. This material is one example of a new class of materials which consist of inorganic crystals containing intercalated organic polymer. The nanocomposite is synthesized by precipitating Ca2Al(OH)6[X]·nH2O (X=OH−, CO3−2) in the presence of poly(vinyl alcohol) (PVA). X-ray diffraction analysis indicates that the nanocomposite consists of calcium aluminate layers separated by interlayers containing anions, water and PVA. The intercalation of PVA can only be accomplished during crystal growth and is accompanied by an expansion in layer spacing from ˜8 Å to ˜18 Å. The nanocomposite exhibited enhanced thermal stability and when compacted into a cylinder was found to have more than twice the compressive strength than the pure calcium aluminate.

Single phase, pure monocalcium aluminate (CaAl2O4) powders are chemically synthesized at temperatures as low as 900°C. The powders have a specific surface area of approximately 10 m2/g. The hydration kinetics of CaAl2O4 and the morphology of the hydrates are analyzed using electron microscopy techniques

Polyphosphates of the general formula NanH2PnO3n+1·H2O, n = 6, 15, 70, where n is the average degree of polymerization, have been synthesized and characterized by 31P NMR and HPLC. Aqueous solutions of these polyphosphates react at room temperature with magnesia to form cement pastes that harden to amorphous materials. The compressive strengths and porosities obtained are similar to those of MgO-(NH4)H2P3O10-H2O cements. Although polyphosphate chain length does not have a significant effect on the strength of the cement, 31P MAS-NMR spectroscopy showed that the degree of polyphosphate chain degradation decreases as the average degree of polymerization, n, increases.

Zeolites can be synthesized in mixtures containing 80 wt% Class F fly ash and 20 wt% ordinary Portland cement if they are mixed with a concentrated NaOH solution and cured at temperatures of 60–90° C. Zeolite Y and NaP-type zeolite were grown in situ in a coexisting calcium silicate hydrate matrix. Those samples made with NaOH, which contained the zeolites, had higher compressive and flexural strengths than equivalent samples made with water.

The studies reported herein were designed to develop a better understanding of the influence of different crosslinking agents on the polymerization of acrylamide gel systems and upon the resulting physical properties of the composites. Specimens were developed via a gel-casting process for viscoelastic and diametral tensile strength testing and the chemical reactions were monitored by Raman spectroscopy and isothermal calorimetry. The studies have demonstrated the ability to tailor the properties of a gel-cast system over a relatively wide range of reaction rates and the resulting mechanical properties by utilizing small adjustments to the overall chemistry of the system.

DSP is made from heavily superplasticized cement combined with microsilica and relatively small amounts of water. In this paper it is shown that substitution of fine-grained rutile for microsilica results in a workable DSP mix.

A comparison of the TGAs, XRDs, SEMs, mercury intrusion porosimetry, and compressive strengths between the two DSP preparations is reported. The results indicate that the DSP made with rutile has very similar properties to DSP made with microsilica.

Variations in the mechanical properties of wood fiber reinforced cementitious (WRFC) materials containing treated fiber and water soluble polymers were investigated. Flexural strength is greatly improved by the addition of polymer. The interface bonding is enhanced by the fiber pre-treatment. The mechanism responsible for the strength increase in WRFC was studied by mercury intrusion porosimetry. Experimental results indicate that the increased strength results from an enhancement in the strength of the interface and reduced porosity.

The effect of starting materials on the synthesis of tobermorite was studied using29Si MAS and CPMAS NMR Spectroscopy. Three Q2 and one Q3 peak were identified during the crystallization of tobermorite from C-S-H. C-S-H, which had a Ca/Si ratio >1, crystallized readily because this C-S-H consists of dimer and short chains of silica tetrahedra. This occurred whenever quartz was used as a starting material. C-S-H, which had a Ca/Si ratio <1 was harder to crystallize because this C-S-H consists of long and cross-linked chains of tetrahedra. The latter was observed when amorphous silica was used as a starting material.

Materials science is the discipline of studying the relationships between structures and properties of materials. In the case of concrete as an engineering material most research has focussed on properties or on microstructure, but only modest progress has been made on establishing relationships between them. In other words a lot of work has been done in the area of strength, fracture toughness [1], shrinkage [2,3], creep and microcracking [2,4], and microstructure each as somewhat isolated subjects [5]. Microstructure has not been related to properties in a quantitative manner.

Conductivity and permittivity of cements were measured during the first 24 h hydration period at 10.0 GHz using front surface reflection methods. Data trends closely followed the hypothesis that the microwave results responded to the transition from free to bound water as hydration proceeded. The results were also compared to measured hydration curves and changes in the slope of the data versus time correlated well with characteristics regions of the hydration curve. The results establish the usefulness of microwave characterization for the study of chemistry and structure during the hydration period and may lead to a non destructive test method for cementitious materials during the early curing period.

The electrical conductivity of portland cement paste is an important transport property, especially since, when properly normalized by the pore fluid conductivity, it is equivalent to the normalized ionic diffusivity of the material via the Nernst-Einstein relation. This paper presents experimental and computer simulation results for σ/σo, where σ is the conductivity of the bulk paste as determined from impedance spectroscopy, and σo is the conductivity of the pore solution. Comparison between simulation and experiment is carried out for an 0.5 water:cement ratio white cement paste as a function of capillary porosity. The quantitative agreement between theory and experiment is reasonable.

In portland cement mortar and concrete, interfacial zones exist around the aggregate particles that have larger pore sizes and pore volumes than the bulk cement paste. If there are enough aggregate particles present, these zones may overlap so as to percolate. A computer simulation model has been developed that can predict this percolation point as a function of interfacial zone thickness, volume fraction of aggregates, and aggregate particle size distribution. The model was used to simulate 1cm3 of mortar, using approximately 10,000 aggregate particles. Results from this model are used to explain recent mercury porosimetry results on mortars having a variety of sand contents. The implications of interfacial zone percolation for the transport properties of mortar and concrete are discussed.

Measurements of the bulk electrical properties of cement pastes were made using impedance spectroscopy (IS) and are useful for studying hydration. Normalization of these quantities by dividing out changes in the pore fluid reveals information pertinent to the microstructural development of these materials. In this study, observations are made on the influence of accelerators, retarders and silica fume (SF) on pastes of white and ordinary portland cements (OPC). All systems show variations in the normalized electrical properties at the same degree of hydration, as compared to a control. Changes in the microstructure that are implied by these measurements are consistent with the observations of others.

Using backscattered electron images, it is shown that an expansive clinker is polymineralic in nature, with individual particles containing the constituents (lime, anhydrite and anhydrous calcium sulphoaluminate) to form ettringite on hydration. The hydration reaction with time of a simple paste of a mixture of this expansive clinker with Ordinary Portland Cement (OPC) has been monitored using backscattered electron images, and the formation of ettringite and a change in the morphology of the calcium hydroxide formed from the added free lime from the expansive clinker is observed. Thermal analysis studies on pastes of the pure expansive clinker have confirmed this apparent change in morphology.

Fracture mechanisms in calcium aluminate macro-defect-free-cement were studied by in situ deformation in the TEM. Fracture occurred predominantly at the cement / polymer interface. The toughening mechanism involved crack bridging at the interphase / polymer interface. XPS studies of the chemistry of the interphase revealed it to be made up of an AlOC complex in addition to the amorphous hydration product phase.

A method is described for carrying out image analysis on portland cements in which the differing chemical compositions of the particles are specifically recognized. Representative fields of ca. 100 individual particles are imaged by a backscatter detector in an SEM, then ported to the attached image analyzer. After preliminary procedures, the image analyzer takes control of the SEM and individually rasters over each particle in turn to acquire both chemical (EDX) and geometrical information. The recorded EDX spectra are used to automatically assign each particle to its predominant mineralogical phase At the same time, conventional feature analysis parameters are acquired for each particle, including measurements of area, length, width, perimeter, shape, etc. The results of the analysis of a given cement constitutes a data base of all of the particles analyzed. It can be used to provide global characterization, or features can be broken out by size class, mineralogical type, shape, or various combinations of parameters. Illustrations are provided of the results of such analysis for a cement, and possible applications to clinker, cement paste, and concrete are considered.

Pore Reduced Cement (PRC) is a high density, high strength material which may have specialist use in the construction industry. It is produced by the high pressure processing of Ordinary Portland cement (OPC) pastes, or blends of OPC with certain supplementary cementing materials, such that effective water/cement ratios (w/c) are significantly reduced relative to those used for mixing. A previous paper [1] describes the mechanical properties of PRC (patent pending) during the early stages of product development and more recent data show that improved preparative techniques are leading to increasing densities and strengths. However, fundamental data on the microstructure, mineralogy and durability properties have not previously been reported. The present paper is directed towards the study of microstructural development in the closely compacted matrix using electron microscopy. Mineralogical and porosity data are also presented.

This paper highlights the physico-chemical characteristics of cementitious materials responsible for or involved in setting, and how these are related to the strengthening and mechanical properties. Five main mechanisms which can be used to increase cementitious materials strength were discussed. The substantially improved cement matrix materials can be obtained by deliberately using one or more above mechanisms. Experiments have been performed on ordinary portland cements and phosphate cements used as construction materials, whose setting time is several hours, and dental cement, whose setting time is several minutes.