High-performance concretes are made with carefully selected high-quality ingredients and optimized mixture designs; these are batched, mixed, placed, compacted and cured to the highest industry standards. Typically, such concretes will have a low water-cementing materials ratio of 0.20 to 0.45. Plasticizers are usually used to make these concretes fluid and workable. High-performance concrete almost always has a higher strength than normal concrete. However, strength is not always the primary required property. For example, a normal strength concrete with very high durability and very low permeability is considered to have highperformance properties. Bickley and Fung (2001) demonstrated that 40 MPa (6,000 psi) highperformance concrete for bridges could be economically made while Fig. 17-1. High-performance concrete is often used in bridges (left) and tall buildings (right). (70017, 70023) High-performance concrete (HPC) exceeds the properties and constructability of normal concrete. Normal and special materials are used to make these specially designed concretes that must meet a combination of performance requirements. Special mixing, placing, and curing practices may be needed to produce and handle high-performance concrete. Extensive performance tests are usually required to demonstrate compliance with specific project needs (ASCE 1993, Russell 1999, and Bickley and Mitchell 2001). High-performance concrete has been primarily used in tunnels, bridges, and tall buildings for its strength, durability, and high modulus of elasticity (Fig. 17-1). It has also been used in shotcrete repair, poles, parking garages, and agricultural applications. High-performance concrete characteristics are developed for particular applications and environments; some of the properties that may be required include:

High performance concrete

Green concrete: Prospects and challenges

Activated blends of Portland cement and fly ash with a high ash content (>70%) are a new alternative to traditional OPCs. A number of papers have been published on C–S–H and N–A–S–H, the two gels that constitute the main cementitious products generated by the alkaline activation of these cements, and the elements that may be taken up into their structure. Very little is known about the kinetics of these systems, however, particularly during the early stages of the reaction. The present study used isothermal conduction calorimetry to explore hydration kinetics during the first 72 h in a cement containing 30% OPC and 70% fly ash. Two activating solutions were used: a mix of NaOH + Na 2 SiO 3 and a Na 2 CO 3 solution. The findings showed that hydration kinetics were substantially modified by the type of alkaline activator used, particularly with respect to the secondary phases generated. In both cases the main reaction product appeared to be a mix of C–A–S–H and (N,C)–A–S–H gels, whose proportions were clearly impacted by the type of activator used.

Hydration kinetics in hybrid binders: Early reaction stages

The synergistic effects of using several supplementary cementitious materials (SCMs), such as Blast Furnace Slags plus Limestone Filler or Fly Ashes, depend on the OPC composition. When using an OPC which is poor in C3A and alkalis in ternary formulations, a similar initial strength gain to that of a plain OPC is detected and at longer hydration ages, the formation of monocarboaluminate, hemicarbonate and hydrotalcite instead of monosulphate can be seen. If an OPC with a higher C3A content and alkalis is used with SCMs, the higher availability of Al causes the early formation of monocarboaluminate and a lower initial strength gain. At longer hydration times, in ternary blends with both OPCs, the mechanical strengths are higher and the C-S-H gels formed are richer in Al and poorer in C/S ratio with a subsequent lowering of the alkali content in the pore solution when compared to that in plain OPC.

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Ordinary Portland Cement composition for the optimization of the synergies of supplementary cementitious materials of ternary binders in hydration processes

The popularity of concrete has been accompanied with dreadful consumptions that have led to huge carbon footprint in our environment. The exhaustion of natural resources is not yet the problem, but also the energy that is needed for the fabrication of the natural materials, in which this process releases significant amount of carbon dioxide (CO2) emissions into the air. Ordinary Portland Cement (OPC) and natural aggregates, which are the key constituents of concrete, are suggested to be recycled or substituted in order to address the sustainability concern. Here, by-products have been targeted to reduce the carbon footprint, including, but not limited to, fly ash, rice husk ash, silica fume, recycled coarse aggregates, ground granular blast-furnace slag, waste glass, and plastic. Moreover, advanced approaches with an emphasis on sustainability are highlighted, which include the enhancement of the hydration process in cement (calcium-silicate hydrate) and the development of new materials that can be used in concrete (e.g., carbon nanotube). This review paper provides a comprehensive discussion upon the utilization of the reviewed materials, as well as the challenges and the knowledge gaps in producing green and sustainable concrete.

https://www.mdpi.com/2071-1050/11/19/5145/pdf

Green Concrete: By-Products Utilization and Advanced Approaches

This research was primarily conducted to verify the presence of synergistic effects in ternary cementitious systems containing portland cement (OPC), class C fly ash (FA) and silica fume (SF). A subsequent objective of the study was to quantify the magnitude of the synergy and to determine its source. For a ternary mixture containing 20% FA and 5% SF by mass, the synergistic effect was observed mostly at later ages (7 days onward) and it resulted in an increased compressive strength and resistance to chloride ion penetration as well as a reduced rate of water absorption (sorptivity) compared to predictions based on individual effects of FA and SF in respective binary systems. The observed synergy was attributed to both chemical and physical effects. The chemical effect manifested itself in the form of an increased amount of hydration products. The physical effect associated with packing density was, somewhat contrary to general belief, not due to an optimized particle size distribution of the binder components of the ternary cementitious system. Instead, it was the result of smaller initial inter-particle spacing caused by lower specific gravities of both FA and SF which, in turn, led to a lower volumetric w/cm. If the mixture design was adjusted to account for these differences, the physical effect would be diminished.

Investigation into the synergistic effects in ternary cementitious systems containing portland cement, fly ash and silica fume

Over the past 30 years, with the advent of computers and digital imaging, many automated systems have been introduced for the purpose of air-void characterization. The majority of the systems employs a contrast-enhancement procedure where a polished cross-section of concrete is darkened with paint, and white powder is forced into the depressions left by air-voids. The system described here follows the same approach and uses a flatbed scanner to collect a single digital image of the entire sample. For all of the systems based on contrast enhancement, the first step is to select a threshold level. Image pixels brighter than the threshold level represent air and image pixels darker than the threshold level represent non-air (i.e., paste or aggregate). Further digital processing steps may be employed but the initial selection of threshold level exerts a strong influence on whether a pixel in the final data set is classified as air or non-air. A systematic approach for threshold determination has been proposed based on an iterative procedure that compares automatically determined air-void parameters to manually determined air-void parameters from a set of training specimens. The calibration procedure finds a single optimum threshold level for the automated system that is to be used for all subsequent analyses. The approach was tested on a population of 88 specimens with manually determined air-void parameters, with the goal of determining an appropriate value for the number of training specimens.

The Practical Application of a Flatbed Scanner for Air-Void Characterization of Hardened Concrete

This research was conducted to verify whether the semi-automatic method of air-void system characterization (using a flatbed scanner) could be used in lieu of the manual (ASTM C457) method. This research objective was accompanied by evaluating the critical air-void system parameters required to ensure freeze-thaw resistance of ternary concrete containing ordinary portland cement (OPC), 20 % of fly ash (FA), and 5 % of silica fume (SF). It was observed that, due to adverse effect of high superplasticizer dosage on air-void system quality (particularly on specific surface), the majority of high slump ternary mixtures exhibited poor freeze-thaw resistance, even if spacing factor was below the 0.20 mm recommended value. However, when the ternary mixtures were prepared with slump below the limit commonly specified for bridge deck applications (190 mm), the critical air-void system parameters of the OPC/FA/SF concrete were comparable to those typically associated with adequate quality air-void system in conventional concrete. Furthermore, since the critical value of specific surface was independent of slump (i.e., superplasticizer dosage), specific surface appeared to be more objective and reliable predictor of freeze-thaw resistance than spacing factor. When comparing the semi-automatic and manual methods of air-void system characterization, a reasonably strong agreement was obtained for such parameters as air content, void frequency, and spacing factor. Although the results of these methods did not match perfectly, the data suggested that the flatbed scanner technique could be efficiently used for discerning between freeze-thaw durable and non-durable concretes.

Evaluation of the Critical Air-Void System Parameters for Freeze-Thaw Resistant Ternary Concrete Using the Manual Point-Count and the Flatbed Scanner Methods

The applicability of the maturity method for prediction of the resistance of concrete to chloride ion penetration as measured by the ASTM C1202 Rapid Chloride Permeability Test was examined. Predictive capability of the method was successfully validated for laboratory-made, continuously moist cured ternary concrete containing 20% fly ash and 5% silica fume and was found to be excellent. Applicability of the developed maturity method was also verified for field-made and field-exposed ternary concrete used during a two-phase construction of a pilot high-performance concrete bridge deck in Indiana. Although agreement between the predicted and measured coulomb values was good for Phase 2 (constructed in spring), the rapid chloride permeability (RCP) values for Phase 1 (constructed in late fall) were consistently underestimated. Reasons for these disparities were thoroughly investigated. It was concluded that the measured values were higher than the predicted ones mainly because of the reduced degree of cement...

Mateusz Radlinski

Papers

Investigation into the synergistic effects in ternary cementitious systems containing portland cement, fly ash and silica fume

The Practical Application of a Flatbed Scanner for Air-Void Characterization of Hardened Concrete

Evaluation of the Critical Air-Void System Parameters for Freeze-Thaw Resistant Ternary Concrete Using the Manual Point-Count and the Flatbed Scanner Methods

Development and Application of Maturity Method for Prediction of Concrete's Resistance to Chloride Ion Penetration