M.R. Silsbee

Effect of silica fume, metakaolin, and low-calcium fly ash on chemical resistance of concrete

Effects of aggressive chemical environments were evaluated on the mortars prepared with ordinary portland cement (OPC) and silica fume (SF)/metakaolin (MK)/low-calcium fly ash at various replacement levels. The natural adverse chemical environmental conditions were simulated using sulfuric acid, hydrochloric acid, nitric acid, acetic acid, phosphoric acid, and a mixture of sodium and magnesium sulfates. Chemical resistance information was used in conjunction with compressive strength measurements to propose realistic OPC/mineral admixture proportions.

Sulfoaluminate-belite cement from low-calcium fly ash and sulfur-rich and other industrial by-products

The study describes the preparation and characterization of an environmentally friendly cement with performance characteristics similar to those of Portland cement, from a lime kiln bag house dust, a low-calcium fly ash, and a scrubber sludge. Promising preliminary results show the formation of relatively low-temperature phases calcium sulfoaluminate (4CaO-3Al 2 O 3 -SO 3 ) and dicalcium silicate (2CaO-SiO 2 ) at ∼1250°C if nodulized raw meal is used for clinker preparation and at 1175°C if powdered raw meal is used as compared to the ∼1500°C sintering temperature required for Portland cement. Phases of the developed cements were predicted using modified Bogue calculations. Isothermal calorimetric measurements indicate the hydration properties of the cements are comparable to ordinary Portland cement. Mechanical properties and microstructural evaluations also were carried out.

Wood fiber surface treatment level effects on selected mechanical properties of wood fiber–cement composites

Abstract The objective of this study was to determine the effects of sodium (N) silicate, potassium (K) silicate, and silane (Si) treatment levels on newspaper and unbleached kraft fibers for enhancing selected mechanical properties of wood fiber–cement composites compared to untreated wood fiber–cement composites. Both wood fiber types were treated with selected aqueous solution strengths, air dried, and mixed with water and cement. The bending and compression properties of the specimens were determined after 28 days of hydration. Results of this study indicated that the aqueous chemical treatments of the wood fibers enhanced some of the mechanical properties of wood fiber–cement composites compared to the untreated wood fiber–cement composites. The enhancement depended on chemical treatment and wood fiber type. All three chemical treatments of newspaper fiber enhanced the normalized toughness values compared to the untreated newspaper fiber–cement composites. In addition, higher treatment levels using N silicate with newspaper fiber improved the compressive strength and bending modulus of the composites compared to the untreated newspaper fiber–cement composites. Kraft fiber treated with all three chemicals enhanced the compressive strength, bending modulus and bending strength compared to the untreated kraft fiber–cement composites. However, only silane-treated kraft fiber improved the normalized toughness values compared to the untreated kraft fiber–cement composites. The results of the study indicated that certain chemical treatments react better with different wood fiber types resulting in selected mechanical property enhancements.

Chloride diffusion in ordinary, blended, and alkali-activated cement pastes and its relation to other properties

Chloride transport into cementitious materials is critical from the viewpoint of protection of reinforcement. This paper is part of a larger study of the characteristics and performance of alkali-activated cementitious materials (AAC) whose properties equal or exceed those of normal Portland cement-based materials. Steady state chloride diffusion studies have been made of pastes of Type I Portland cement, and its blends with different proportions of ground granulated blast-furnace slag. Very substantial reductions in diffusion rates have been found with increased proportion of slag. In addition, alkali activation has been shown to reduce the diffusion rate by at least a factor of two. Other properties determined include: density, porosity, pore size distribution (Hg), BET (N 2 ) surface area, shrinkage, compressive and flexural strength, leaching, alkali-aggregate reaction, and freezing and thawing resistance. Comparisons with results of previous studies and with other blending components are discussed.

Effects of fiber surface treatments on mechanical properties of wood fiber–cement composites

Abstract The purpose of this research was to determine the effects of treated and untreated hardwood, kraft softwood, and newsprint wood fibers on the 7- and 28-day bending strength, compressive strength, and toughness values for wood fiber–cement composites. Untreated and acrylic- or alkylalkoxysilane-treated hardwood, kraft softwood, and newsprint wood fibers used in wood fiber–cement composites resulted in different bending and compression properties. Fiber characteristics along with different chemical treatments influenced the composite properties. Compressive strength decreased for all fiber types and chemical treatments compared to the neat cement controls. Bending strength values for all wood fiber composites were higher than the neat cement control specimens. Both the acrylic emulsion and alkylalkoxysilane treatments provided improvements in the bending strength values compared to the untreated wood fiber–cement composites. Toughness improved for all untreated and treated wood fiber–cement composites compared to the neat cement control specimens. The toughness value results for the alkylalkoxysilane-treated fibers were similar to the acrylic-treated fibers in that the longer kraft softwood fiber–cement composites had the highest toughness values compared to the other fiber groups.

Characterization of silicate sealers on concrete

Sealing concrete with soluble sodium silicate may improve surface properties such as hardness, permeability, chemical durability, and abrasion resistance. Previously, such treated surfaces had not been characterized sufficiently to provide a complete understanding of how silicate improves concrete properties. Therefore, it is the object of this work to contribute to the understanding of how the application of soluble silicate alters the surface of concrete by verifying its effects on absorption, abrasion resistance, chloride permeability, chloride penetration, and surface composition.

Alkali Activated Cementitious Materials: An Overview

Alkali-activated cementitious materials have considerable potential, with properties ranging from very high early strength to very high long term strength and low porosity. The role of alkalis in activating industrial by-products such as ground granulated (glassy) blast-furnace slag, ultra-fine silica fume or other by-product silicas, glassy fly ashes, and other amorphous materials is discussed. These by-product materials are activated by alkali additions which break the strong silicon oxygen bonds in the silicate or alumino-silicate network, accompanied by the formation of new reaction products. The role of the different components in multi-component activated cements on the reactivity and the nature of the resultant products is discussed. Characterization of starting materials and reaction products by XRD, SEM (including environmental SEM), chemical, and particle characterization techniques has been made. Additional results include investigation of pore solution chemistry as a function of time. Some inferences for long term durability are discussed.

Microwave sintering of sulphoaluminate cement with utility wastes

Class C flyash, baghouse dust and scrubber sludge have been successfully used for sulphoaluminate belite (SAB) cement preparation by microwave sintering. For proper raw mix proportioning, the modulus of gehlenite (C2AS)1 formation (MG) and modulus of calcium sulphosilicate (2C2S·CS) formation (MS) were put forward. The results indicated that, when MG and MS were 0.90–1.10, C2AS and 2C2S·CS could be chemically eliminated when microwave-sintered at low temperature; with the 1150°C/10 min sintering condition, microwave-prepared sample had developed into SAB cement clinker with the main phases of C4A3S and β-C2S, while a conventionally fired one had not; with proper gypsum addition, microwave-prepared SAB cement developed strength similar to Type-I cement in 28-day hydration.

Temperature and moisture effects on selected properties of wood fiber-cement composites

The effects of moisture cycling on the dimensional stability and temperature cycling on the compressive strength of treated wood fiber-cement composites were investigated. The Kraft softwood fibers and the hardwood fibers were treated with an aqueous acrylic emulsion or alkylalkoxysilane prior to manufacturing into wood fiber-cement composites. Moisture cycling results indicated that the treated fiber-cement composites were more resistant to deterioration than the neat cement specimens. The alkylalkoxysilane-treated fiber-cement composites resisted deterioration more than the acrylic emulsion-treated fiber-cement composites. Treated hardwood fiber-cement composites were more resistant than the treated Kraft fiber-cement composites. The effects of temperature cycling on the compressive strength values produced similar results. The treated fibers were more resistant to deterioration than the neat cement. The alkylalkoxysilane-treated Kraft and hardwood fiber-cement composites had higher average compressive strength values than the acrylic emulsion-treated wood fiber-cement composites.

Microwave sintering of flyash

Abstract Class F flyash has been sintered by microwave and conventional processes. The sintering was carried out in a temperature range of 800 to 1000 °C. Densities up to 2.2 g/cm 3 , and diametral tensile strength up to 26 MPa (corresponding diametral compressive strength 78 MPa) were achieved after sintering for 10–20 min. The microwave sintered samples were denser and thus stronger than the samples conventionally sintered at the same temperature for the same time. The sintered bodies are glass-ceramic material, with mullite (Al 6 Si 2 O 13 ) as the major crystalline phase.