Proportioning for performance-based concrete pavement mixtures

The work presented in this dissertation involves an effort to develop a mix proportioning tool that can be used to determine the required type and amount of concrete components in a mixture based on the desired fresh and hardened concrete properties. Concrete performance is affected by the quantity and quality of the paste, and aggregate systems. Therefore, this study analyzed the effect of binder systems with different types and content; the paste quality; and size, shape, texture and gradation of different aggregate systems on various fresh and hardened concrete properties. In this experimental program, a total of 178 mixtures were prepared with 7 different gradation systems, 12 binder systems, 25 binder contents, 6 different water-to-binder ratio (w/b), and 3 different nominal air content. Fresh properties of slump, air content, air-void system, setting time, unit weight, and temperature were tested. Hardened properties of compressive strength, rapid chloride penetration, surface resistivity, air permeability, and shrinkage were tested at various ages. However, to develop such a tool, this study overall focused on the assessment of workability, compressive strength, and durability as these three properties are commonly used as indicators of concrete performance. Durability was assessed by testing the rapid chloride penetration, and surface resistivity at 28-days. As part of this study, an artificial neural network (ANN) approach has been used for concrete mix proportion design to analyze the complexity between concrete properties and concrete components. Results have shown that development of a performance-based mix proportioning tool is possible for mixtures when aggregate gradation is not varied. Development of a mix proportioning tool with addition of the various aggregates systems generally was not as successful due to the increased variability of the mix design parameters such as size, shape, texture, and gradation of aggregates. The proposed mix proportioning tool is promising and achievable in terms of predicting the values of the tested properties based on the mix design variables. Although the proposed mix proportioning tool is not completely ready for prime time, the findings of this study can be implemented in real time when this approach is used with a larger data set

Optimizing concrete mixtures with minimum cement content for performance and sustainability

The main purpose of this research is to investigate the minimum cement content required with an appropriate water-to-cement ratio (w/c) to meet given workability, strength, and durability requirements in a concrete pavement; and to reduce carbon dioxide emissions, energy consumption, and costs. An experimental program was conducted to test 16 concrete mixtures with w/c ranging between 0.35, 0.40, 0.45 and 0.50; and cement content ranging from 400, 500, 600 and 700 lb/yd3 (pcy). The fine aggregate-to-total aggregate ratio was fixed as 0.42 and the void content of combined aggregates was maintained the same for all the mixtures. Slump; setting time; 1, 3 and 28-day compressive strength; 28-day chloride penetration; and 1, 3, and 28-day air permeability were determined. The test results showed that strength is a function of w/c and independent of cement content after the required cement content is reached, for a given w/c. Workability is a function of w/c and cement content: increasing w/c or cement content improves workability. Setting time is reduced when cement content is increased for a given w/c. Chloride penetration increases as w/c or cement content increases, when one parameter is fixed. Air permeability increases as cement content increases, for a given w/c. Based on these findings, it is possible to reduce the paste content without sacrificing the desired workability, strength and durability, for a given w/c. When the overall effect of cement content on concrete properties is evaluated, 400 pcy of cement content is not recommended due to its high porosity caused by its low paste content. Furthermore, 700 pcy would also not be appropriate as increasing cement content does not improve the strength, after the required content is reached; and may decrease durability as high cement content both increases air permeability and chloride penetration. Moreover, for a w/c higher than 0.35, cement content of more than 500 pcy adversely affects the concrete performance by decreasing strength (increasing cement content from 500 pcy to 700 pcy approximately reduced the 28-day compressive strength by 15%) and may cause shrinkage related cracking problems. Therefore, for a given w/c and for the aggregate system used in this study, the range of 500 pcy to 600 pcy is found to be the most appropriate cement content range that provides the desired workability, strength, chloride penetration and air permeability. Mixtures with 500 pcy of cement content did not have a high workability (ranging from 0 in. to 3 in. depending on the w/c), but it may be improved by the addition of supplementary cementitious materials, water-reducing agents, or using a different aggregate gradation system. The given cement content range was compared with the values obtained in accordance with the ACI 211 Report (2002): considering the high cement content range of 650 pcy to 930 pcy provided by the ACI 211 Report (2002) for the same given conditions, the recommended cement content range of 500 pcy to 600 pcy will have more significant impact and benefits on the concrete construction industry regarding the reduction of cement content. In addition, to make the findings independent of the selected aggregate system, the relationship between paste volume and concrete properties is established. In order to meet the desired workability, strength and durability requirements; the paste volume should be within the range of 160% to 170% of the volume of voids. Exceeding this range will adversely affect the concrete performance by decreasing strength, and increasing chloride penetration and air permeability

Concrete Pavement Mixture Design and Analysis (MDA): An Innovative Approach To Proportioning Concrete Mixtures

Mixture proportioning is routinely a matter of using a recipe based on a previously produced concrete, rather than adjusting the proportions based on the needs of the mixture and the locally available materials. As budgets grow tighter and increasing attention is being paid to sustainability metrics, greater attention is beginning to be focused on making mixtures that are more efficient in their usage of materials yet do not compromise engineering performance. Therefore, a performance-based mixture proportioning method is needed to provide the desired concrete properties for a given project specification. The proposed method should be user friendly, easy to apply in practice, and flexible in terms of allowing a wide range of material selection. The objective of this study is to further develop an innovative performance-based mixture proportioning method by analyzing the relationships between the selected mix characteristics and their corresponding effects on tested properties. The proposed method will provide step-by-step instructions to guide the selection of required aggregate and paste systems based on the performance requirements. Although the provided guidance in this report is primarily for concrete pavements, the same approach can be applied to other concrete applications as well

Effect of paste-to-voids volume ratio on the performance of concrete mixtures

The purpose of this study is to investigate the minimum paste volume required with an appropriate water-to-cementitious ratio (w/cm) to achieve required workability, strength, and durability requirements of concrete mixtures for pavements. In this experimental program, 64 concrete mixtures with varying w/cm, cementitious content, and binder type were prepared and tested. The fine aggregateto-total aggregate ratio was held constant for all the mixtures. Fresh and hardened concrete properties of the mixtures were determined at various ages. Test results have shown that approximately 1.5 times more paste by volume is required than voids between the aggregates to achieve a minimum performance in concrete for pavements. For a given w/cm, strength is independent of cementitious content after a critical value is provided. When w/cm is constant, increasing paste content increased chloride penetrability and air permeability

Effect of water-to-binder ratio, air content, and type of cementitious materials on fresh and hardened properties of binary and ternary blended concrete

The purpose of this study is to investigate the effects of water-to-binder ratio (w/b), air content, and type of cementitious material on the fresh and hardened properties of binary and ternary blended concrete mixtures in pavements. This experimental program prepared a total matrix of 54 mixtures with w/b of 0.40 and 0.45; nominal air content of 2, 4, and 8%; and three types of supplementary cementitious materials and one ordinary portland cement in different combinations. Binder systems included ordinary portland cement, binary mixtures with slag cement, Classes F and C fly ash, and ternary mixtures containing a combination of slag cement and one type of fly ash.Workability, total air content, air void system parameters (i.e., spacing factor and specific surface) in fresh concrete, setting time, compressive strength, surface resistivity, and shrinkage were determined. Test results showed that ternary mixtures followed the trends of their constituent materials. Binary and ternary mixtures containing Class C fly ash and slag cement exhibited higher compressive strength than the control mixture. The surface resistivity and shrinkage results of binary and ternary mixtures were equal to or improved over the control mixture

Preliminary Investigation on Determining the Minimum Cement Content in Rigid Pavements

This paper presents the preliminary results of an experimental program that consists of testing of concrete mixtures with varying water-to-binder ratios (w/b) and cementitious contents. The purpose of this laboratory study is to investigate the minimum cement content that can be used in rigid pavements without sacrificing the performance (i.e., strength and durability). Initially, 16 mixes using only portland cement and 48 mixes incorporating supplementary cementitious materials, namely class F fly ash, class C fly ash and slag as portland cement replacement at levels of 20%, 20% and 40%, respectively, were planned. This paper reports the results of a subset of this study. Concrete mixtures with w/b ranging from 0.43 to 0.65 and cementitious content ranging from 400 lb/yd3 to 700 lb/yd3 were designed. Compressive strength, chloride penetration and air permeability were determined. The findings of the study with the available data are as follows: strength is a function of w/b and independent of the binder content; air permeability increases as w/b and binder content increase; among all the mixtures containing different type and amount of cementitious materials, slag cement provides the lowest 28 day chloride penetration whereas class C fly ash results in the highest chloride penetration