Cement systems composed of tetracalcium phosphate powder or powder mixtures of tetracalcium phosphate and brushite were investigated. The liquid components for making the cements include aqueous solutions of H3PO4, Ca(OH)2, or Na2SiO3. For the tetracalcium phosphate cement, strong acidic or basic solutions must be used in order to achieve a short setting time.

Our results show that the tetracalcium phosphate and brushite cement can set in a short time under suitable conditions. Humidity, particle size, and pH of liquid have a strong influence on cement setting. Solutions of Ca(OH)2 or Na2SiO3 can be used for making high pH cements and a solution of H3PO4 for a low pH setting cement. To reduce the setting time of cement, the key is to control the hydrolysis of tetracalcium phosphate. The results of hydrolysis indicate that, at 37°C, the single-phase tetracalcium phosphate can only be converted to hydroxyapatite when hydrolyzed in solutions with an H3PO4 solution concentration of ∼5% or with a high pH solution.

Both the single-phase tetracalcium phosphate cement and the mixture phase cement have good biocompatibility. Appropriate concentrations of the solutions of Na2SiO 3,Ca(OH)2, or H3P04 can be used in the cements from the perspective of both biocompatibility and cement properties.

Hard human tissues, teeth, and bone are composite materials. These composites are primarily composed of impure, calcium-deficient hydroxyapatite and collagen. The formula for stoichiometric hydroxyapatite is: Ca10(PO4)6(OH)2. However, this compound exists over a range of compositions that may be characterized in terms of a Ca/P ratio. The Ca/P ratio of stoichiometric material is 1.67. Stable compositions may have Ca/P ratios extending to 1.5:Ca9(PO4)6HOH. Structurally, hydroxyapatite contains two types of calcium sites. Four of the calcium sites per unit cell are each coordinated with 8 oxygens. Six of the calcium sites per unit cell are 7-coordinated. Six of these seven bonds are with oxygens, while the 7th is with a hydroxyl ion. Calcium deficiency results in the formation of up to one vacancy per unit cell on one of these seven coordinated calcium sites. Charge balance is maintained by the removal of one of the hydroxyl oxygens. The remaining proton becomes bound to an oxygen that is also coordinated with a phosphate. As a result, it is common to express the formula of calcium-deficient hydroxyapatite having a Ca/P ratio of 1.5 as Ca9(PO4)5(HPO4)OH.

Reactive aluminas, including rapidly calcined gibbsites, offer exciting potential for forming ceramic materials at low temperatures. New x-ray amorphous aluminas will react with water at room temperatures to form compacts with 10–50 MPa tensile strengths, via viscous slurries. The cementious behavior of these materials has been examined. The results of TGA, x-ray diffraction, SEM, mechanical properties, and other characterization techniques, as applied to these systems, will be discussed.

Pastes prepared from diammonium orthophosphate and calcined magnesia, MgO, exhibit a fast setting and hardening associated with NH3 liberation. Struvite, MgNH4PO4.6H2O, was found to be the main reaction product. Pastes made with NaH2PO4 or Na-polyphosphate exhibit a similar hardening reaction. The hardening reaction may be retarded and the ultimate strength moderately increased by adding appropriate retarders, such as Na2B4O7 10H2O to the system. The quality of the used MgO and its fineness has a significant effect on the rate of the hardening reaction.

In a series of test specimens made out of magnesium phosphate cement, their physico-mechanical properties–i.e., fracture toughness, Poisson's ratio, Young's modulus, and bending strength–were studied. Samples included in the study were either in their original moisture state or dried. Some of them were polished on their tension side to eliminate the effect of surface defects.

Silica-modified portland cement-based Chemically Bonded Composites (CBCs) have been prepared and cured to elevated temperatures. It has been found that when cementitious composites with calcium-to-silica (C/S) ratios of 0.83 are thoroughly hydrated through hydrothermal curing, followed by careful dehydration, mortars of exceptional strength are produced. The bulk of this strength is maintained to over 600°C. X-ray diffraction studies of binder samples dried at 200°C and 500°C show only slight differences in mineral product contents. Above 600°C, a drop in strength is noted, and a substantial portion of the binder converts to wollastonite. Even so, these CBC composites retain as much as 40% of their peak compressive strength to temperatures up to 800°C. Applications of these materials in high-temperature industrial processes are presented.

Cement-based materials have been traditionally formed by casting. The amount of water used in the casting process determines the porosity of the hardened material. The water requirements, and the tendency for cement grains to agglomerate, result in hardened cement paste having high porosity and a wide range of pore sizes. Consequently, such materials are not very strong and contain critical flaws whose dimensions are of the order of 0.1 mm. Although improvements in particle packing and particle dispersion to reduce porosity have resulted in significant increases in strength, such materials are still very brittle and have relatively low tensile and flexural strengths.

The fracture toughness of MDF (macro-defect-free) cement with different polymer contents has been investigated by the indentation-strength method and fracture surface analysis. It was found that the fracture toughness obtained by these two different techniques showed good agreement for the low (3 wt.%) polymer cement. The ultimate (apparent) toughnesses are 1.3 Mpam1/2 for low polymer content and 2.2 Mpam1/2 for high (8 wt.%) polymer content cement. Different microcracking and sponge-like microstructures have been observed and discussed.

It is becoming more generally accepted that the role of the polymers in these MDF (macro-defect-free) cement systems is more complex than simply acting as a processing aid or a filler. The polymer interacts in some way with the cations released from the cement to form a metal cross-linked polymer gel. Studies on complex formation in polymer gels have shown that there is often an unusual specificity in the ions, resulting in the highest degree of complexation. In addition, gel formation often occurs only within a narrow pH regime. Hence, the results shown here will attempt to examine the effects of altering the cement chemistry on strength development in calcium silicate-based systems.

The automated analysis of backscattered SEM images from polished surfaces of macro-defect-free cements based on ordinary portland cements is examined. A comparison of several techniques for the determination of pore size distributions in these materials is made.

Calcium aluminosilicate glass cements that hydrate directly to stratlingite (2CaO·Al2 O3 SiO2 · 8H2 O) and/or hydrogamet solid solution (3CaO·Al2 O3·XsiO2 ·[16–2X]H2O) are described.

Hydrogamet develops rapidly during curing of pastes containing between 12 and 16 wt.% SiO2, while stratlingite grows more slowly in bladed radial spherulites in compositions containing 18 to 25% SiO2

Compressive strengths between 35 and 70 MPa, 20–35% porosity, and excellent thermal and chemical stability are characteristic of the cured hydrogamet cements, while the stratlingite pastes have strengths between 70 and 140 MPa and 1–10% porosity.

A preferred composition area is described that yields mixtures of the two hydrated phases, resulting in a useful combination of low porosity and high early strength.

Highly reactive alumina (from Rhone-Poulenc), which is x-ray amorphous, offers a great potential as a new Al-source precursor for forming low-temperature chemically bonded ceramics. This alumina has been characterized for the first time. Its thermal behavior, structure, morphology, and hydration behavior have been determined using XRD, TGA, DTA, SEM, and TEM, and the data are compared with those of other conventional aluminas and precursors such as α-Al2O3, gibbsite, and boehmite.

The hardening shrinkage of calcium aluminate based ultra-high strength cement becomes nearly zero by using calcium sulphoaluminate compound, and very high bending strength can be obtained by calcinating at 300°-600°C. The starting materials are calcium aluminate, silica fume, calcium sulphoaluminate compound and superplasticizer, and the water-to-power ratio is 0.15–0.25. The main hydration products are C3AH6, AH3, C-S-H and ettringite, forming a densely packed structure, together with a large amount of unreacted cement particles. The hardening shrinkage is remarkably reduced, because of the ettringite formation in the early stage. The bending strength is about 55 MPa when calcined at 600°C. C12A7 is identified by XRD; needle-shaped skeletons of ettringite crystals are observed by SEM. It is suggested that chemically bonding substances are C12A7, amorphous A12O3, and C-S-H in calcined calcium aluminate based DSP with ettringite.

The advantage of utilizing blended cements for many applications has been well documented. However, the use of these materials has been limited by the longer setting times associated with the use of these materials. This report discusses the development of formulations employing alkali activation to shorten the setting times. The results of characterization of these materials using calorimetry, microscopic, x-ray diffraction, and mechanical property techniques are discussed.

Ultrafine Alkali Activated Slag (AAS) and Portland/Slag (P/S) cements have been commercially available in the United States for 2 and 5 years, respectively. Ultrafine cements have been the subject of research at Northwestern University for 6 years.

Particle size of the ultrafine slag cement is characterized by 98% passing at 7 microns and a D50 at 3 microns in contrast to the ultrafine portland/slag cement which has 98% passing at 10 microns and a D50 at 4 microns.

The chemical composition of the slag used in these cements is 35% SiO2, 16% Al2O3, and 43% CaO. The composition of the portland/slag cement, which is a 25/75 blend, is therefore between the bulk composition of portland cement and the slag.

Both of the ultrafine cements permeate fine sands when formulated at high water-to-cement ratios. Viscosity plays an important part in the permeation mechanism, and both cements exhibit viscosities below 10 cps at water-to-cement ratios of 2. This low viscosity is obtained through the use of superplasticizing with naphthalene sulfonate and acrylic acid polymers.

Applications of the ultrafine cements include dam grout curtain rehabilitation, consolidation grouting, and nuclear and hazardous waste containment. One hundred and twenty metric tonnes of the portland/slag cement have been used for hazardous waste containment at Niagara Falls, New York.

In this paper an active β-C2S was used to prepare compacted and polymerized pastes with low porosity. X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and tri-methy silanation-gel permeation chromatography (TMS-GPC) techniques were used to characterize the microstructure of the pastes both before and after additions of inorganic complexing ions, Fe2+ and Ni2+, and organic silane VTES.

The results indicate that both inorganic complexing ions and organic silane can play a role in the polymerization of the native silicate anions in the cement pastes. These materials lead to a distinct increase of pentamer, octamer, and polymer components in the pastes, resulting in a decrease in the average C/S ratio in the C-S-H phase. The samples obtained from this processing have very high mechanical strengths, up to a compressive strength of 316 MPa, and fracture surface energy of 43 J/m2.

The substitution of Al into the structure of tobermorite was investigated, along with the resultant phase assemblages that compatibly coexist with the Al-tobermorite. All experiments were conducted under hydrothermal conditions at saturated steam pressure. The temperatures of the experiments varied from 90° to 190°C and times from 1 to 28 days. Ca/Si ratios varied from 0.7 to 1.7, Al/(Al+Si) from 0.12 to 0.30. NaOH varied from none to 5 moles/mole tobermorite constituents. X-ray diffraction was used not only to identify phases but to determine degree of substitution and the rate of approach to steady state.

Maximum Al substitution was found to be Al/(Al+Si) = 0.13, and the maximum interlayer spacing was 11.42 ± 0.015 Å. This is in agreement with previously published work which found a trace of hydrogarnet at Al(Al+Si) = 0.15 and a maximum interlayer spacing of 11.45 ± 0.02 A. When Al concentrations in the mix are greater than enough to make maximum Al-tobermorite, “low”-hydrogarnet (“low”-hydrogarnet has ∼0.1 SiO2 per mole). As Al concentration is raised, a variable composition hydrogamet is formed and then a “high”-garnet of constant composition (SiO2 = 0.7 moles/mole hydrogarnet) is formed.

NaOH was found to have a major effect on the kinetics and the phase assemblages at a given time. Al-tobermorite, although stable at 90°C, converts to xonotlite at 175°C in the absence of NaOH. In its presence, even at a level too low to make Na-containing phases, Al-tobermorite persists at 21 days at 175°C. In the absence of NaOH, at 175°C, Al-tobermorite forms at up to 7–10 days but is converted to xonotlite at 28 days. Coexisting phases are gyrolite and cowlesite at Ca/Si ≥ 1 and hillebrandite and “low”-garnet at Ca/Si > 1. When there is enough NaOH to form Na-containing phases, Al-tobermorite coexists with reyerite and analcime at Ca/Si > 1. At Ca/Si < 1 and Al less than the composition on the tie line between Al-tobermorite and “low”-garnet, Al-tobermorite coexists with “low”-garnet and portlandite. In the compatibility triangle between Al-tobermorite, “low”-garnet, and “high”-garnet, Al-tobermorite coexists with variable Si-gamet. When Al exceeds its limiting value on the tie line, Al-tobermorite-“high”-gamet, the assemblage is Al-tobermorite-“high”-gamet-cowlesite.

Polymer-modified cement concrete represents a heterogeneous material whose properties are influenced more by the properties of the polymers than by the properties of the cement component. Typical of polymeric materials are their temperature dependent behavior. This temperature dependence can be related to the glass transition temperature of the polymer. In cases where the temperature is higher than the glass transition temperature, strength decreases while deformability simultaneously increases. Polymeric films are formed in the dispersed polymer systems as a result of reactions occurring at the glass transition temperature. A styrene/acrylic modified concrete was studied at different polymer loadings. The tensile and compressive strengths of this system were studied as a function of temperature. Increasing deformability temperatures principally at higher polymer loadings near the glass transition temperature and decreasing strength occurred.

Water glass Na2O-SiO2 reacts in water solutions with Na2SiF6, yielding an amorphous SiO2 and NaF. This reaction, that is completed within a few days, causes setting and hardening of the system. Mortars made with this binder using appropriate fillers sustain temperatures of up to 900°C. At temperatures above 500°C, the hardened material converts gradually to tridymite quartz and sodium disilicate. Above 900°C, a sodium fluosilicate glass melt starts to be formed.