Showing papers on "Silica fume published in 2011"

Ultra-High Performance Concrete with Compressive Strength Exceeding 150 MPa (22 ksi): A Simpler Way

Abstract: Although intensive research related to ultra high-performance concrete (UHPC) and its composition has been conducted over the past 2 decades, attaining compressive strengths of over 150 MPa (22 ksi) without special treatment, such as heat curing, pressure, and/or extensive vibration, has been nearly out of reach. This paper describes the development of a UHPC with a compressive strength exceeding 200 MPa (30 ksi), obtained using materials commercially available in the U.S. market and without the use of any heat treatment, pressure, or special mixer. The influence of different variables such as type of cement, silica fume, sand, and high-range water reducer on compressive strength is evaluated. The test results show that the spread value, measured through a slump cone test on a flow table, is a good and quick indicator to optimize the mixture packing density and thus its compressive strength.

Utilization of silica fume in concrete: Review of hardened properties

Abstract: Several types of industrial byproducts are generated. With increased environmental awareness and its potential hazardous effects, utilization of industrial byproducts has become an attractive alternative to disposal. One such by-product is silica fume (SF), which is a byproduct of the smelting process in the silicon and ferrosilicon industry. Silica fume is very effective in the design and development of high strength high performance concrete. This paper covers the physical, chemical properties of silica fume, and its reaction mechanism. It deals with the effect of silica fume on the workability, porosity, compressive strength, splitting tensile strength, flexural strength, creep and shrinkage of concrete.

Utilization of silica fume in concrete: Review of durability properties

Abstract: With increased environmental awareness and its potential hazardous effects, utilization of industrial byproducts has become an attractive alternative to disposal. Silica fume (SF), which is byproduct of the smelting process in the silicon and ferrosilicon industry. Silica fume is very effective in the design and development of high strength high performance concrete. This paper covers the physical, chemical properties of silica fume, and its reaction mechanism. It deals with the effect of silica fume on the permeability, freezing and thawing resistance, corrosion, sulfate resistance, carbonation, and alkali-aggregate resistance of concrete.

Pozzolanic properties of fine and coarse color-mixed glass cullet

Abstract: Mixed glasses of different colors are economically difficult to reuse for the fabrication of new glass products but their use in cement-based materials is a promising way to recycle this material. This paper deals with the pozzolanic activity of mixed glass cullet, by evaluating the pozzolanic behavior of a large range of glass particle sizes, from less than 40 μm (540 m2/kg) up to 2.5 mm (2.2 m2/kg). Five different classes of glass are assessed separately, in terms of compressive strength tests on mortars, consumption of lime (TG), morphology (SEM) and composition of hydrates (EDX and X-ray fluorescence). The results show that the pozzolanic activity increases with glass fineness and that, compared to a reference material without glass, equivalent or superior compressive strength can be obtained when using up to 40% of glass of 540 m2/kg fineness. A transition fineness around 30 m2/kg (140 μm) is highlighted, for which the pozzolanic activity becomes substantial. However, a slight but significant pozzolanic activity is detected for coarse particles (>1 mm), as confirmed by the consumption of Ca(OH)2, the formation of C–S–H-like hydrates and an increase of 10% (5 MPa) in the compressive strength compared to an inert admixture. The chronology of the reaction (pozzolanic and alkali-reactive) for coarse glass particles is discussed.

Single and combined effects of nano-SiO2, nano-Al2O3 and nano-Fe2O3 powders on compressive strength and capillary permeability of cement mortar containing silica fume

Abstract: In this article, the single, binary and ternary effects of three nano-sized powders of the main oxides of cement (nano-SiO2, nano-Al2O3 and nano-Fe2O3) on the compressive strength and capillary permeability of cement mortars containing silica fume were investigated. The powder amounts were chosen at proportions corresponding to 0.5%, 1.25% and 2.5% of the binder amount. Compressive strength was determined for early age (3- and 7-day), standard age (28-day), and late age (56- and 180-day) mortars, while capillary permeability was determined for 180-day-old mortars only. It was concluded from the experimental results that the type and amount of nano the powders, and mortar production methods had a significant effect on the fresh and hardened properties of cement mortars. The nano-powders used singly or in combination increased the 28-day compressive strength of silica fume-containing mortars by up to 27%, with the exception of nano-SiO2 powder used at a proportion of 2.5%. However, the compressive strength values fluctuated at early and later ages. The best results for compressive strength and capillary permeability at the end of day 180 were obtained with 1.25% nano-Al2O3 powder in single uses, 0.5% nano-SiO2 + nano-Al2O3 powders in binary combinations, and 0.5% in ternary combination. However, it was determined that the interaction between the powders used in binary and ternary combinations led to negative effects on the physical–mechanical properties of the mortars. For this reason, nano-Al2O3 powder and single use were primarily recommended in cases where an increase in the performance of cement-based composites is desired. The findings of the experiments suggested the conclusion that the improvement in the mechanical and physical properties of mortars was caused by the rise in pozzolanic activity induced by the favorable influence of the powders rather than the filler effect.

Alkali–Silica Reaction: the Influence of Calcium on Silica Dissolution and the Formation of Reaction Products

Abstract: In a model system for alkali―silica reaction consisting of microsilica, portlandite (0-40 mass%), and 1M alkaline solutions (NaOH, KOH), the influence of calcium on silica dissolution and on the formation of reaction products is investigated. The reaction and its products are characterized using calorimetry, X-ray diffraction, thermogravimetric analysis, nuclear magnetic resonance, desorption experiments, and pore solution analysis in combination with thermodynamic modeling. Silica dissolution proceeds until portlandite is consumed due to the formation of C-S-H, and subsequently, saturation of dissolved silica in the alkaline solution is reached. As a result, the amount of dissolved silica increases with the increasing portlandite content. Depending on the amount of portlandite added, the reaction products show differences in the relative amounts of Q 1 , Q 2 , and Q 3 sites formed and in their average Ca/Si ratio. The ability of the reactions products to chemically bind water decreases with the decreasing relative amount of Q 3 sites and with the increasing Ca/Si ratio. However, the amount of physically bound water in the reaction products reaches a maximum value at a Ca/Si ratio between 0.20 and 0.30.

Performance of sewer pipe concrete mixtures with portland and calcium aluminate cements subject to mineral and biogenic acid attack

Abstract: The paper reports on the performance of a series of sewer pipe concrete mixtures and cementitious lining mixtures in acid environments. Binder types based on ordinary portland cement (OPC) and calcium aluminate cement (CAC) were used, with both acid-soluble and acid-insoluble aggregates and various supplementary cementitious materials (SCM). One series of tests subjected the mixtures to pure mineral acid (hydrochloric acid, pH = 1), using a specially designed dynamic test rig. The other series of tests involved monitoring specimens placed in a live sewer under very aggressive conditions induced by acid-generating bacteria. Under mineral acid attack on concretes with conventional dolomite aggregates, OPC/silica fume concretes displayed best performance, attributed to their densified microstructure coupled with substantially improved ITZ. CAC concretes with dolomite aggregate did not perform any better than similar OPC specimens under these conditions, primarily because of their higher porosity. However, with concretes using synthetic alagTM aggregates in mineral acid testing, CAC/alagTM mixtures performed exceptionally well due to their homogeneous microstructure, inferred absence of an ITZ, and slower dissolution and finer size of alagTM aggregate particles. The dynamic acid test was able to reveal differences in physical and chemical interactions between constituents in concrete mixes. Under biogenic acid conditions in the sewer, CAC concretes clearly outperformed OPC concretes. This is ascribed to the ability of CAC to stifle the metabolism of the acid-generating bacteria, thereby reducing acid generation. Thus the effects of neutralisation capacity and stifling of bacterial activity need to be distinguished in designing concrete mixtures to provide good acid resistance. Relative rates of dissolution of binder and aggregates are also important in overall performance, with uniform rates preferable in order to avoid aggregate fallout.