Mix Design Parameters Research Articles

Effect of binder content on the performance of alkali-activated slag concretes

This paper assesses the mechanical and durability performance of concretes produced using alkali silicate-activated ground granulated blast furnace slag as sole binder. Alkali-activated concretes are formulated with 300, 400 and 500 kg slag per m 3 of fresh concrete, and their performance is compared with reference concretes produced using Portland cement (OPCC). Regardless of the binder content, the alkali-activated slag concretes (AASC) develop higher compressive strength than the comparable reference concretes. A higher binder content leads to increased strength in both AASC and OPCC at 28 days. However, at 90 days, the performance penalty for low binder content is more significant in the OPCC than AASC samples. Permeability, water sorption and carbonation resistance properties are also improved at higher binder contents. By controlling mix design parameters, it is possible to produce AASC with mechanical strength and durability comparable to conventional Portland cement concretes.

Effect of coarse aggregate characteristics on concrete rheology

In the present study, concrete was considered as a two-phase material, consisting of coarse aggregate (CA) and mortar. Coarse aggregate properties were characterized by fineness, uncompacted void and friction angle. The combined effects of CA characteristics and mix design on the rheological properties of the corresponding concrete were investigated using a portable IBB concrete rheometer. Experimental results indicated that a higher CA and fine aggregate content normally result in higher concrete rheological parameters (yield stress and viscosity). For a given type and amount of mortar, concrete yield stress and viscosity generally increase with the uncompacted void content and friction angle but decreased with the size (or fineness) of CA. Well graded CA, generally having low uncompacted void content, provides concrete with considerably reduced yield stress and viscosity when compared with single-sized CA. In addition, a multiple-parameter linear regression analysis was conducted to evaluate how different CA characteristics (fineness, uncompacted void and friction angle) and mix design parameters (mortar composition, and CA volume fraction) affect concrete rheological behavior.

Experimental Investigation of Ultrasound Wave Focusing in Attenuative Solids

This paper presents an experimental study on ultrasonic focusing in an attenuative solid made of cement mortar. The objective is to comparatively investigate the performance of various techniques for wave focusing. Standard attenuation measurements are performed on small cement mortar samples to generate a preliminary idea about the loss in the material. Subsequently, focusing experiments are conducted on a larger mortar block fabricated with the same mix design parameters. The time-delayed and time-reversal methods are employed to perform focusing. A synthetic aperture approach is used to generate the unfocused and focused fields. The time-reversal focusing method generates a narrower focal spot in comparison to the time-delayed method, indicating better focusing action. The experimental results are also compared with an analytical model of focusing in an attenuative fluid with an array of point sources, and a good agreement is confirmed.

Identification of microstructural characteristics in lightweight aggregate concretes by micromechanical modelling including the interfacial transition zone (ITZ)

An approach which combines both experimental techniques and micromechanical modelling is developed in order to characterise the elastic behaviour of lightweight aggregate concretes (LWAC). More than three hundred LWAC specimens with various lightweight aggregate types (5) of several volume ratios and three different mortar matrices (normal, HP, VHP) are tested. The modelling is based on iterative homogenisation process and includes the ITZ specificities experimentally observed with scanning electron microscopy (SEM). In agreement with experimental measurements, the effects of mix design parameters as well as of the interfacial transition zone (ITZ) on concrete mechanical performances are quantitatively analysed. Confrontations with experimental results allow identifying the elastic moduli of LWA which are difficult to determine experimentally. Whereas the traditional empirical formulas are not sufficiently precise, predictions of LWAC elastic behaviours computed with the micromechanical models appear in good agreement with experimental measurements.

A Measurement Approach for Critical Voids in Mineral Aggregate Based on AC-20

The voids in the mineral aggregate (VMA) is considered to be the most important mix design parameter which affects the durability of the asphalt concrete mix. This has traditionally been addressed during mix design by meeting a minimum voids in the mineral aggregate (VMA) requirement, based solely upon the nominal maximum aggregate size without regard to other significant aggregate-related properties. The goal of this study is to determine the validity of the minimum VMA requirement versus nominal maximum aggregate size required in Marshall volumetric mix design. Specimens were compacted using the Superpave Gyratory Compactor (SGC), conventionally tested for bulk and maximum theoretical specific gravities and physically tested using the thiaxial creep test system under a repeated load confined configuration to identify the transition state from sound to unsound. AC-20 was classified in the light of fine, dense and coarse gradation. The AC-20C, AC-20D and AC-20F asphalt mixtures were tested as the object of study. The results clearly demonstrate that the volumetric conditions of an VMA mixture at the stable unstable threshold are influenced by a composite measure of the aggregate size gradation .The currently defined VMA criterion, while significant, is seen to be insufficient by itself to correctly differentiate sound from unsound mixtures. Under current specifications, many otherwise sound mixtures are subject to rejection solely on the basis of failing to meet the VMA requirement. Based on the laboratory data and analysis, a new paradigm to volumetric mix design is proposed that explicitly accounts for aggregate gradation factors.

Evaluation of Environmental Effectiveness of Titanium Dioxide Photocatalyst Coating for Concrete Pavement

Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed with air-cleaning agents with a super-hydrophilic photocatalyst such as titanium dioxide (TiO2). Although this technology has the potential to support an environmentally friendly road infrastructure, several design and operational parameters may affect its effectiveness and need to be evaluated. The objective of this study was to evaluate the environmental and mix design parameters that may affect the effectiveness of the environmental performance of TiO2 coating. An experimental program was conducted: the effects of relative humidity level, flow rate of pollutants, and mix design parameters, including contents of TiO2 and aggregate sizes, were investigated. The environmental efficiency of the samples to remove nitrogen oxides from the atmosphere was measured by using a newly developed laboratory setup. Results of the experimental program showed that the mix designs without fines achieved the highest photodegradation rates. In addition, the increase from 3% to 5% TiO2 resulted in little improvement in the nitrogen oxide removal efficiency, which decreased with the increase in the humidity level and the pollutant flow rate.

Characterizing the Relaxation Modulus Properties of HMA Mixes Based on the Uniaxial Strain-Controlled Testing

ABSTRACT Relaxation Modulus (RM) is one of the mechanical properties that can be utilized to model the visco-elastic behavior of Hot-Mix Asphalt (HMA) for various purposes including material response analysis, design, and performance prediction. In this study, the uniaxial static strain-controlled RM tests conducted at three temperatures of 10, 20, and 30 °C were used to characterize the time-dependent elastic relaxation modulus (E(t)) and stress relaxation rate (m) of various commonly used Texas HMA mixes. The effects of various mix-design parameters including asphalt-binder type, content, and modifier; aggregate type; and oxidative aging on both the E(t) and m parameters were also investigated and are discussed in this paper. A total of thirteen different HMA mixes were tested. Test data variability and consistency are also discussed including some suggestions for the RM test protocol improvements.

Fresh, Mechanical, and Durability Characteristics of Self-Consolidating Concrete Incorporating Volcanic Ash

Self-consolidating concrete (SCC) is known for its excellent deformability, high resistance to segregation, and use in congested reinforced concrete structures characterized by difficult casting conditions without applying vibration. The use of known mineral admixtures such as fly ash and slag cement has proved very effective in the production of nonexpensive SCC with satisfactory fresh and hardened properties. However, the use of volcanic ash (VA) in SCC is new and can provide low cost SCC. This paper presents fresh, mechanical, and durability characteristics of VA based SCC mixtures (VA-SCCs). VA-SCCs are developed by varying water-to-binder ratio, percentages of VA as cement replacement, and dosages of superplasticizer (SP). Mix design parameters are optimized to achieve minimum use of SP and optimum use of VA. The fresh concrete properties are determined from slump flow, V-funnel flow time, bleeding, air content, and segregation tests. The mechanical properties and durability characteristics such as compressive strength, freezing-thawing resistance, rapid chloride permeability, surface scaling resistance, and drying shrinkage are determined to evaluate the performance of VA-SCCs. The study produces encouraging results and confirms the production of satisfactory VA based SCC mixtures with acceptable properties. VA-SCCs having a minimum strength of 15 MPa (requirement for some structural concrete applications) can be obtained by replacing up to 50% (by mass) of cement by VA. Development of nonexpensive and environmental friendly VA-SCC with acceptable strength and durability characteristics (as illustrated in this study) is extremely helpful for the sustainable development and rehabilitation of volcanic disaster areas around the world.

Field Evaluation of Asphalt Film Thickness as a Design Parameter in Superpave Mix Design

Research shows that asphalt film thickness (AFT) is related to mix performance. The use of AFT as a mix design parameter has always been a challenge because of the complexity of estimating AFT based on mix parameters. The aggregate surface area and the effective volume of asphalt are important components in the calculation of AFT. This study compares the voids in mineral aggregate (VMA) and AFT as mix design parameters against the field performance of Superpave mixes. Film thickness was estimated by different formulas using calculated aggregate surface area. Data on early flushing sections of Superpave mixes was used to correlate film thickness to distress development and other mix design parameters. The pavement sections considered for the study were observed to have undergone flushing and rutting problems. Field cores from flushed and non-flushed sections were obtained and verified for compliance with Superpave specifications. The results of this research related AFr to mix design parameters but showed that depending on the method of calculation, AFT, as a mix design parameter, mayor may not be helpful in explaining specific field performance distresses such as rutting or bleeding.

Correlation between compressive strength and certain durability indices of plain and blended cement concretes

In this study, plain, silica fume and fly ash cement concrete specimens prepared with varying water to cementitious materials ratio and cementitious materials content were tested for compressive strength, water permeability, chloride permeability, and coefficient of chloride diffusion after 28 days of water curing. The data so developed were statistically analyzed to develop correlations between the compressive strength and the selected durability indices of concrete. Very good correlations were noted between the compressive strength and the selected durability indices, particularly chloride permeability and coefficient of chloride diffusion, irrespective of the mix design parameters. However, these correlations were observed to be dependent on the type of cement.

Binder Flushing in Low Traffic Volume Superpave Mixes

This paper analyzes early flushing or ”bleeding” that occurred in several sections of Superpave pavement designed for low traffic volume roads in Nebraska. The objective of this study was to develop a better understanding of the causes of flushing and to examine the relationship between flushing and the material specifications for low traffic volume Superpave mixes. Records indicate that construction of the flushed sections proceeded within specifications. Moreover, all QA/QC material test results were within acceptable ranges. A review of mix design parameters for all flushed sections was conducted to verify compliance with Superpave specifications. Comparison of specified parameters between flushed and non-flushed sections with identical mix designs were also conducted. Field samples from flushed and non-flushed sections were obtained and analyzed for mix design verification and binder characterization. Additional testing on recovered asphalt binders was conducted to assess binder contribution to flushing. Results indicated that recovered binder properties did not meet Superpave specifications. This research shows the compatibility of asphalt binder dominates the asphalt-aggregate interaction. Flushing in the affected pavement sections resulted from excessive binder content, variations in binder properties due to poor material quality control, and lack of a requirement to test for separation problems during construction.

Dry-cast concrete masonry products: properties and durabilityThis article is one of a selection of papers published in this Special Issue on Masonry.

Performance of dry-cast concrete masonry products (DCCMPs), which are becoming the product of choice for many applications, has yet to be assessed in a comprehensive manner. This study was undertaken to investigate the effects of mix design and manufacturing parameters on the mechanical and transport properties, as well as the freeze–thaw (F/T) durabilities, of DCCMPs. The variables studied were water to cement ratio, mixing time, vibration time, and curing regime. Freeze–thaw durability was assessed in accordance with the American Society for Testing and Materials (ASTM) standard C1262 by exposing specimens to four conditions: water, 3% NaCl, 4% CaCl2, and 4% MgCl2 solutions. Results revealed that 3% NaCl exposure yielded the most mass loss due to scaling, whereas 4% MgCl2 exposure exhibited the least. Increase in either water content, vibration time, mixing time, or use of moist curing led to improvement in the mechanical properties, refinement of large pores in the range of 40 to 400 μm, reduction of total porosity, and enhancement of F/T durability of capstones. Ionic sorptivity yielded a strong statistical correlation with mass loss due to F/T action in the presence of 3% NaCl and 4% CaCl2.

Calibration of Nonnuclear Density Gauge Data for Accurate In-Place Density Prediction

Hot-mix asphalt (HMA) density is an important acceptance quality characteristic, which involves in situ tests for quality control and assurance (QC/QA). Highway agencies have conventionally used nuclear density gauges or core samples for mat density. More recently, alternate nondestructive testing methods have been considered to replace current test methods. Nonnuclear density gauges offer rapid testing while eliminating safety risks and costs associated with radioactive license. Although agencies have evaluated them, they are not implemented in acceptance testing so far. Results are presented from a field evaluation of three nonnuclear density gauges—PaveTracker, PQI 300, and PQI 301—conducted on Wisconsin Department of Transportation (WisDOT) paving projects. The main goal was to evaluate the performance and effectiveness of non-nuclear gauges for use in QC/QA activities by WisDOT. The study involved field tests at 16 project sites and included 21 mix designs and a variety of mix design and pavement design parameters, such as aggregate type, nominal maximum aggregate size, layer thickness, design traffic, and base type. Density measurements were recorded at 30 test points at each site with one nuclear gauge and three nonnuclear gauges. Although the mean standard deviation values of the nonnuclear gauge data were less than those of the nuclear gauge measurements, a consistent bias was observed between the two data sets. This bias was adjusted by using a calibration factor to yield density predictions statistically the same as the nuclear gauge measurements. It is recommended that a calibration factor determined from 10 points by using a slope function be implemented for agency use. Further, daily calibration for each mix design is recommended when the project involves multiple paving days.

An updated look at drying shrinkage of Portland and blended Portland cement concretes

National and overseas reports clearly show that a significant proportion of concrete construction problems are associated with drying shrinkage. These results could be a result of few available long-term drying shrinkage data and changes of the behaviour of concrete mixes used nowadays. Therefore, poor estimates of drying shrinkage strains from prediction models could impair the performance and service life of concrete structures. The objective of the current research was to analyse the effect of mix design parameters on drying shrinkage of concretes made with Portland and blended Portland cements, considering 30 mixes that are commonly used in local construction, tested up to 1350 days of drying. It was concluded that, when using rapid-hardening cement of any type, a larger maximum aggregate size and lower water content reduces drying shrinkage. Cement and aggregate type are shown to have a significant effect on drying shrinkage time function and magnitude. Experimental results were compared with calculated drying shrinkage strains estimated by ACI 209, CEB MC90, B3, GL 2000, Sakata 1993 and Sakata 2001 models. It was concluded that none of the shrinkage prediction models adequately reproduced the observed shrinkage behaviour of concrete made with Chilean Portland and blended Portland cements, underestimating the actual long-term drying shrinkage strains.

Development of Mix Design Procedure for Cold In-Place Recycling with Foamed Asphalt

The main objective of this study is to determine mix design parameters for cold in-place recycling with foamed asphalt. First, the foaming process of laboratory foaming equipment was validated by varying the water and asphalt content. 1.3% water content was adopted to create the optimum foaming characteristics in terms of the expansion ratio and the half-life at 170°C under air pressure of 400 kPa and water pressure of 500 kPa. The mix design was then performed using both the indirect tensile test and the Marshall test for 13 combinations of foamed asphalt content and water content for three different gradations. The water content did not appear to affect the test results significantly. Maximum stability (both wet and dry samples), maximum bulk density, and indirect tensile strength (both wet and dry samples) were all obtained around 2.5% foamed asphalt content. Overall, the highest Marshall stability and indirect tensile strength were obtained in the order of fine, field, and coarse reclaimed asphalt pavement gradations. It is recommended that the indirect tensile strength based on wet samples be adopted for determining the optimum foamed asphalt content.

Comparative Analysis of Field Permeability Testing of Compacted Hot-Mix Asphalt Pavements: Using Air and Water Permeameters

The in-place permeability of asphalt pavements has been the focus of recent research as investigators try to establish links between pavement permeability and performance. Previous research concluded that pavements with in-place air voids exceeding 8% to 10% may be considered as excessively permeable, and it is generally accepted that excessively permeable pavements are more prone to oxidation and stripping of the asphalt binder, as well as more susceptible to freeze-thaw degradation. As the use of the Superpave® design procedures has increased, numerous questions have arisen regarding the effect of certain mix design parameters on the in-place density and permeability of compacted asphalt pavements. A recent investigation into this issue has generated the need for reliable test methods and equipment that can be used to assess the field permeability of in-place pavements. Results of field permeability tests conducted on newly constructed asphalt pavements by using both water and air permeameters are prese...

Comparative Analysis of Field Permeability Testing of Compacted Hot-Mix Asphalt Pavements

The in-place permeability of asphalt pavements has been the focus of recent research as investigators try to establish links between pavement permeability and performance. Previous research concluded that pavements with in-place air voids exceeding 8% to 10% may be considered as excessively permeable, and it is generally accepted that excessively permeable pavements are more prone to oxidation and stripping of the asphalt binder, as well as more susceptible to freeze–thaw degradation. As the use of the Superpave® design procedures has increased, numerous questions have arisen regarding the effect of certain mix design parameters on the in-place density and permeability of compacted asphalt pavements. A recent investigation into this issue has generated the need for reliable test methods and equipment that can be used to assess the field permeability of in-place pavements. Results of field permeability tests conducted on newly constructed asphalt pavements by using both water and air permeameters are presented. The data obtained indicate that currently accepted test methods based on the water permeameter may not produce repeatable results for all pavement types investigated. In contrast, test data obtained with the air permeameter indicate good repeatability for all included pavement types.

Recycled aggregates concrete: aggregate and mix properties

This study of structural concrete made with recycled concrete aggregate focuses on two issues: 1. The characterization of such aggregate on the Spanish market. This involved conducting standard tests to determine density, water absorption, grading, shape, flakiness and hardness. The results obtained show that, despite the considerable differences with respect to density and water absorption between these and natural aggregates, on the whole recycled aggregate is apt for use in concrete production. 2. Testing to determine the values of basic concrete properties: mix design parameters were established for structural concrete in non-aggressive environments. These parameters were used to produce conventional concrete, and then adjusted to manufacture recycled concrete aggregate (RCA) concrete, in which 50% of the coarse aggregate was replaced by the recycled material. Tests were conducted to determine the physical (density of the fresh and hardened material, water absorption) and mechanical (compressive strength, splitting tensile strength and modulus of elasticity) properties. The results showed that, from the standpoint of its physical and mechanical properties, concrete in which RCA accounted for 50% of the coarse aggregate compared favourably to conventional concrete.

CDW recycled aggregate renderings: Part II – Analysis of the effect of materials finer than 75 μm under accelerated aging performance

Quality control of the performance of renderings made up of construction and demolition waste (CDW) recycled aggregates needs to be improved as CDW recycling can prove to be an alternative to waste disposal in developing countries. This experimental work focuses the effectiveness of a mix design method to control and analyze the recycled aggregate composition influence on the performance of mortars and renderings. Leveling time in the placement of renderings was also studied. The mix design method of mortars takes into account two parameters: the “aggregates and plasticizing materials to cement ratio” and “the total materials finer than 75 μm” in the dry mortar. In Part I of this study [Construction and Building Materials, submitted to publishing] the basic properties of mortars of several mixes were analyzed for a constant cement content around 155 ± 10 kg/m 3. The performance of renderings is the scope of Part II of this paper. The initial bond strength and visible drying cracks under laboratory conditions were first analyzed for renderings applied on masonry panels with two times of leveling during placement. After five months, accelerated aging of renderings was carried out. Ten wetting–drying cycles upon thermal shock, from 80 °C to laboratory room temperature, were applied to the masonry panels, and cracks were assessed for each cycle. Bond tensile strength was not affected by the thermal shock, but additional cracks were seen on the renderings. The mix design parameters of the mortars and their hardened state properties were related to the cracking of the renderings. The results show that the parameters “total materials finer than 75 μm” and “aggregate to cement ratio” can be used for the mix design of mortars with recycled CDW aggregates. The increase in tensile strength and the reduction in the content of total fines smaller than 75 μm have proved efficient parameters to control cracking of renderings under thermal shock. Leveling time during rendering placement was a secondary parameter for cracking behavior.

C-φ Characterization Model for Design of Asphalt Mixtures and Asphalt Pavements

Abstract This paper reports the results of a research effort initiated in the early 1990s to develop a C-φ (cohesion-angle of friction) characterization model for the design of asphalt mixtures and asphalt pavements. It is demonstrated that, since the model is based on the fundamental material properties represented by C and φ, it can derive analytically other asphalt mix design parameters such as Marshall stability and flow, and indirect tensile strength. The C-φ characterization model therefore offers a useful basis for the development of a comprehensive design framework that integrates asphalt mix design with asphalt pavement structural design. To demonstrate this capability, the research developed an empirical-mechanistic rutting prediction model of asphalt pavement layer using the C-φ characterization model. In addition, the model allows stresses and strains under design loading to be computed, which can be applied as input to structural analysis for asphalt material selection and pavement thickness design.