Performance-based Specifications Research Articles

Using construction procurement strategy to achieve socioeconomic development objectives

The procurement strategy for a construction project should provide the framework to achieve secondary procurement and socio-economic development objectives [2]. However, little attention has been focused on this in theory and practice. This paper addresses that gap by presenting a case study of the innovative targeting strategy developed and successfully implemented on a New Universities Project in South Africa to promote specified socioeconomic development objectives. Document analysis was used to examine how four socioeconomic development targets or key performance indicators, namely: local employment, skills development, local expenditure, and B-BBEE, were contractually integrated into the main works contracts. Four out of five framework contractors achieved the development targets, with low-performance damages applied in one case where the contractor failed to achieve all the development targets. The findings demonstrate how an appropriate construction procurement strategy that effectively integrates the packaging, targeting, and contracting strategies with effective systems for monitoring performance-based specifications, can play an essential role in promoting and realising socio-economic development objectives and social value through infrastructure projects.

Progress towards sustainability through performance-based standards and specifications

Specifications for cement and other concrete-making materials have been largely prescriptive and have evolved from the user needs for consistent quality and the producer needs for uniform requirements across markets. Performance criteria such as strength requirements or setting time are used in some cases, but specifying other material properties in terms of performance has not been common. By definition, a prescriptive specification has a limited scope and focuses on key characteristics of a narrow range of materials. The result is that prescriptive specifications often provide barriers to use of alternative, more sustainable material combinations and as we work to attain specific sustainability goals, prescriptive specifications often are counter-productive to achieving those goals. Barriers to new materials may stem from the specification limits or the tests used to measure key properties, or both. A prescriptive approach was adequate when the choice of materials was limited, which has been the case historically. However, over the past 50 years, enormous progress has been made in concrete technology permitting combinations of materials that did not exist 50 years ago. Current specifications, however, still reflect the materials used in that bygone era. To address these issues, standard specifications and tests are evolving and industry is moving towards performance-based standards. Examples of these advancements will be discussed along with remaining challenges.

A Performance-Based Design Framework for Enhanced Asphalt Concrete in the Caribbean Region

The majority of recent research in has been focused on the introduction, development, and evaluation of performance-based specifications for the design of asphalt concrete mixtures. In the Caribbean, most laboratories only use the Volumetric Marshall Mix design methodology. Road designers, engineers, consultants, and contractors have all highlighted the many shortcomings and inadequacies of the volumetric design mix selection process. The consensus is that there is a need to a develop process that addresses the service’s performance and common distress on asphalt pavements through performance-based mix design. Performance-Based Mix Design (PBMD) has been used as a practical alternative to the volumetric mix design technique in evaluating pavement distresses by incorporating performance testing in conjunction with volumetric parameters into the mix design process. This study describes the findings of our comprehensive laboratory research, which was conduced to facilitate the development of a Performance-Based Mix Design framework for asphalt concrete mixtures. The research methodology involved the collection and integration of qualitative and quantitative data through case studies and experimental work. Two control and two PBMD mixtures were designed to evaluate both the volumetric and performance properties that address distresses of permanent deformation (rutting), fatigue cracking, stiffness, and moisture susceptibility. The PBMD framework led to the development of performance test criteria for permanent deformation, stiffness modulus, fatigue cracking, and an acceptable tensile strength ratio. The development and implementation of the PMBD framework for the Caribbean region could exemplify a significant step towards achieving sustainable asphalt pavements in the region. The framework, which incorporates best-practice solutions, is anticipated to increase awareness about the variables that affect the performance of asphalt mixtures.

Towards performance-based specifications for fly ash and natural pozzolans – Insights from a Monte-Carlo based thermodynamic modeling framework

Monte-Carlo-based thermodynamic modeling framework is used to assess the chemical limits set by ASTM C618-23. Realistic chemistries and reactivities for supplementary cementitious materials (SCMs) and chemistries for cement are generated using statistical data from the literature. 200,000 thermodynamic simulations are performed for each cement+SCM system to evaluate performance through Ca(OH)2 content, capillary porosity, and C-S-H volume. The results indicate that the reactivity of SCMs is directly related to its performance in paste, and its inclusion in ASTM C618 would be beneficial for optimized utilization of SCMs in performance-based mixtures. When providing chemical limits for SCMs, separating the reactive pozzolanic oxides (RPO) from bulk oxide composition is critical for paste performance. Fe2O3 content did not significantly impact the performance. If RPO is specified, fly ashes and natural pozzolans could have similar chemical limits. SCMs can be classified based on CaO and SO3 contents to affect Ca(OH)2 and AFt in paste, respectively.

Case Studies of Asphalt Pavement Quality Assurance Specifications, Performance-Related Specifications, and Performance-Based Specifications

Quality assurance (QA) specifications for asphalt pavement construction measure quality characteristics to adjust payments. The measured quality characteristics are assumed to empirically relate to performance. The validity of this assumption, however, has been questioned in recent years; thus, there has been increased interest in finding ways to more directly evaluate the performance of the as-constructed materials. One proposed method to meet this need involves using the Asphalt Mixture Performance Tester (AMPT) and its associated test methods, which measure fundamental material properties that are then used to calculate the fatigue cracking performance index, Sapp, and a rutting strain index (RSI). These indices can be used in performance-related specification (PRS) or performance-based specification (PBS) frameworks to determine the pay adjustments during the construction of asphalt pavement. While PBS requires measured indices, PRS uses index-volumetrics relationships (IVRs) to predict Sapp and RSI based on conventional acceptance quality. Payment can then be based on a percent within limits (PWL) approach. This paper demonstrates how pay adjustments can be made for a paving project in Indiana following three different QA specification frameworks: the current QA specifications framework in the Indiana Department of Transportation, a PRS framework using IVRs, and a PBS framework that employs measured Sapp and RSI. For each framework, the main elements of the specification were identified and determined. The specification limits for Sapp and RSI and weight factors in composite pay factor equations were determined such that the resulting pay factors are comparable to pay factors obtained from the current QA practices.

Features of immittance spectra as performance indicators for cement-based concretes

Design for durability and performance-based standards and specifications for reinforced concrete infrastructure is limited by the lack of rapid, science-based test methods for characterising the deterioration resistance of concrete. In this paper, this issue is addressed though the application of two-point electrical impedance measurements taken within the frequency range 100 Hz–10 MHz. Data are presented for a range of industry-standard cement-based concrete mixes with and without supplementary cementitious materials. Nyquist plots (−iZ″(ω) against Z′(ω)) and Bode plots (Z*(ω) and θ against frequency) clearly highlight the frequency dependence of the electrical response. However, when presented in the form of permittivity and conductivity, a region of dispersion was evident over the entire frequency range for all concretes. The features of this response, which could be gainfully exploited as durability indices for assessing the long-term performance of concrete, are identified and discussed. A range of formalisms is presented and it is shown that, within this frequency range, conductivity was found to obey Jonscher's universal power law. Two novel durability parameters are presented based on features of Jonscher's model; from a practical viewpoint, the power-law model can be evaluated using conductivity measurements obtained at three, easily measured, spot frequencies (10 kHz, 1 MHz and 10 MHz).

Integrating Quality Assurance in Balance Mix Designs for Durable Asphalt Mixtures: State-of-the-Art Literature Review

Delivering durable asphalt concrete within a reasonable cost is one of the great ambitions of pavement material engineers. This state-of-the-art review article documents the efforts spent in the past two decades to ensure the durability and performance of asphalt mixtures in mix design and production. A perspective with the attempt to integrate laboratory mix design, plant production quality assurance, and field place acceptance is applied in the review. The development of the performance specification and performance mix design is summarized. The paper categorizes performance specification into index-based performance specification and predictive performance specification that include performance-related specification and performance-based specification. The approaches to developing index-based performance mix design/balanced mix design and predictive performance mix design are also compared in the review. The challenges and solutions in incorporating performance tests in asphalt productions are documented and discussed. The challenges include selecting performance testing methods, determining index threshold limits, estimating and incorporating testing variability and uncertainty, determining sampling position and testing frequency, and so forth. The paper also provides suggested areas of future research and implementation activities.

Development of a Tool for Determining Optimal Material Blends for Unpaved Road Wearing Courses

Experience over more than 100 years has shown that the appropriate choice of materials used on unpaved road wearing courses is critical for ensuring good and safe performance. Despite the availability of internationally developed performance-based specifications for unpaved road wearing course materials that will meet most requirements, many road agencies continue to use empirical specifications comprising grading envelopes and plasticity index ranges that do not provide an indication of expected performance. This complicates choosing the optimal blends of more than one material to obtain a better performing unpaved road wearing course, or determining the quantities of supplemental materials and the recycling depth when converting distressed, low-volume, paved roads to an engineered unpaved road standard. This paper introduces a performance-based approach to selecting unpaved road wearing course materials and a tool for optimizing blends of materials to meet specifications. The tool can be used in manual calculations, but rapid results can be obtained by using a web-based tool. The tool can be used for new unpaved road construction, regraveling existing unpaved roads, or for converting distressed paved roads to an engineered unpaved road standard. The tool is a companion to another tool that can be used for selecting chemical treatments for unpaved roads. It should be noted that the results from the tool are dependent on accurate input values for materials and road layer thickness, and consequently project investigations and materials testing are encouraged. Estimated values are likely to give misleading outputs.

Probabilistic selection and design of concrete using machine learning

Abstract Development of robust concrete mixes with a lower environmental impact is challenging due to natural variability in constituent materials and a multitude of possible combinations of mix proportions. Making reliable property predictions with machine learning can facilitate performance-based specification of concrete, reducing material inefficiencies and improving the sustainability of concrete construction. In this work, we develop a machine learning algorithm that can utilize intermediate target variables and their associated noise to predict the final target variable. We apply the methodology to specify a concrete mix that has high resistance to carbonation, and another concrete mix that has low environmental impact. Both mixes also fulfill targets on the strength, density, and cost. The specified mixes are experimentally validated against their predictions. Our generic methodology enables the exploitation of noise in machine learning, which has a broad range of applications in structural engineering and beyond.

An assessment of a practical implementation of the deemed-to-satisfy durability design and specification approach in the Swakopmund-Walvis Bay Freeway upgrade project in Namibia

Steel corrosion in reinforced concrete (RC) structures in the marine environment is a major concern for engineers and asset managers. This paper presents an assessment of the application of a deemed-to-satisfy durability design and specification approach on the newly constructed RC bridges on the Swakopmund-Walvis Bay Freeway upgrade in Namibia, with a desired service life of at least 100 years. The deemed-to-satisfy design and specification approach comprised a combination of South African recommendations for binder type, minimum binder content and w/b ratio, EN 206-1 recommendations for cover depth, and South African National Roads Agency Limited (SANRAL) durability index targets along with on-site concrete quality control guidelines on placement, compaction and curing. As-built concrete durability properties (i.e. water sorptivity, oxygen permeability and chloride conductivity) and cover depth were measured and used to check (using a Fickian-based service life model) if the deemed-to-satisfy specifications were adequate. The results showed that the as-built concrete durability properties surpassed the deemed-to-satisfy durability performance targets, while the on-site cover depth values showed significant inadequacies in some bridge elements. The service life estimations showed that the deemed-to-satisfy durability performance specifications were adequate. Considering the relatively high concrete quality achieved on site, it is clear that the 100-year service life could have been achieved more sustainably using a good balance of concrete quality and cover depth [e.g. a lower concrete quality (using less cement) or lesser coved depth] if a more rigorous performance-based durability design and specification approach had been used. Ultimately, the service life analyses using the as-built concrete model input parameters highlight not only the critical importance of both concrete quality and cover depth in achieving durable RC structures prone to steel corrosion, but also the inherent limitations of the deemed-to-satisfy durability design and specification approach.

Evaluation of unbound/subgrade material rutting and resilient behaviour based on initial density and saturation degree

Unbound pavements with thin surface seals constitute the majority of the lightly and moderately trafficked road networks in Australia. In such pavements, it is considered that seals do not offer much structural support, whereas most of the load coming from the traffic is supported by unbound granular materials and subgrade soil. Hence, accurate estimation of the mechanical properties of such materials is crucial for the satisfactory performance of pavements. In the present study, a constant radial stiffness triaxial (CRST) test was performed on a silty sand, which is typical of the material used in subbase and subgrade layers. The major advantage of the CRST test over the conventional repeated load triaxial test is that the confining pressure is dynamically applied due to a constant radial stiffness boundary condition. It is argued that the CRST test better replicates the stress path typically encountered by geo-materials under the action of traffic loading on pavements. A laboratory investigation was undertaken with different initial dry densities and degree of saturations to develop empirical models of plastic strain (rutting), resilient modulus and Rvalue. Based on the models developed, isograms of these aforesaid parameters are drawn on the compaction plane for the first time and a method is conceptualized for compaction control during field construction providing pathways to performance-based compaction specification.

African Case Studies: Developing Pavement Temperature Maps for Performance-Graded Asphalt Bitumen Selection

The reliable performance of roads is crucial for service delivery, and it is a catalyst for domestic and cross-border spatial development. Paved national roads are expected to carry higher traffic volumes over time as a result of urbanization and to support the economic development in the continent. Increased traffic levels combined with expected increases in air temperatures as a result of global warming highlight the need to appropriately select bituminous road materials for a reliable performance of asphalt roads. The objective of the paper is to present African case studies on the development of temperature maps necessary for performance-graded bitumen selection for road design and construction. A consistent approach, that caters for the variability of geographical, environmental and climatic conditions, does not currently exist within the continent. Therefore, this paper discusses a series of critical components in the development of temperature maps for performance-graded bitumen including (i) pavement temperature models and climatic zones in Africa; (ii) the effect of urban heat islands on pavement temperature; (iii) sources of weather data and (iv) the mapping procedure to produce temperature maps. Characterizing the thermal properties of the pavement was found to be an important factor for reliably calculating expected road temperatures as well as the consideration of the ambient climate for a given location. During this study, the urban heat island effect was found to have little influence on the maximum pavement temperatures but a significant effect on the minimum pavement temperatures. Some areas of the urban district assessed in this investigation were found to increase by two performance grades according to the minimum temperature criteria. The recent observed weather data from weather stations are the most accurate means of measurement of the ambient environmental conditions necessary for performance-based specifications, but they are not always easily accessible, and therefore other sources of data, such as satellite data, may need to be used instead. With the expected temperature increases expected as a result of climate change, the use of Global Climate Models also opens new avenues for performance-based material selection in the African continent for expected climates as an alternative to traditional approaches based on historically observed weather.

A state-of-the-art review of compaction control test methods and intelligent compaction technology for asphalt pavements

This paper investigates the current state of knowledge of the existing compaction testing methods for asphalt and identifies the limitations of these methods in using them during asphalt pavement compaction. Conventional spot tests that are carried out at limited spots for quality control (QC) and quality assurance (QA) of asphalt compaction often fail to ensure the uniformity of compaction. The differential approach using microwave sensors attached to the rollers can qualitatively indicate the optimum density during asphalt compaction; however, it requires spot density measurements to quantify the asphalt density achieved. intelligent compaction (IC) can be used to ensure the uniformity of asphalt compaction and to get real-time feedback. The current IC specifications for soil compaction are not suitable for asphalt compaction due to the viscoelastic nature of asphalt and the variation of asphalt mat temperature during compaction in the field. In addition, the state-of-the-art intelligent compaction measurement value (ICMVs) recorded during asphalt compaction does not correlate well with the asphalt density while it shows a reasonable correlation with asphalt stiffness. The effects of asphalt mat temperature and underlying support on ICMVs measured by IC rollers are identified as the potential causes of the poor correlation between ICMVs and spot density measurements. It is proposed that the relationship between asphalt modulus used in pavement designs and the ICMVs corrected for the effects of asphalt mat temperature and underlying support needs to be investigated in order to establish performance-based specifications for QA/QC of asphalt compaction. The emerging research on using GPR for asphalt density estimation is examined and the factors that affect the GPR measurements during asphalt pavement compaction are identified .

Validation of Performance-Based Specifications for Surface Asphalt Mixtures in Virginia

The Virginia Department of Transportation (VDOT), like many owner agencies, is interested in ways to facilitate the increased durability of asphalt mixes in an effort to make its roadway network more sustainable, longer lasting, and more economical. The balanced mix design (BMD) method proposes to address this through the incorporation of performance criteria into mix design and acceptance. VDOT has committed to the implementation of the BMD method in an effort to improve asphalt mix performance. The purpose of this study was to continue advancing efforts toward implementation of BMD through the evaluation of 13 asphalt mixes using performance-indicating laboratory tests, validation of the initial performance tests selected for BMD use, and validation of the initial test threshold criteria. Based on the results, the asphalt pavement analyzer (APA) rut test, indirect tensile cracking test (IDT-CT), and Cantabro test were found suitable for continued use in BMD. The current threshold criteria for all three tests were found reasonable based on additional mix testing. The study recommends that APA rut test and IDT-CT results should be compared and correlated to fundamental rutting and cracking tests, respectively, as well as to performance predictions obtained from mechanistic-empirical pavement design simulations, and to field performance for full assurance that test threshold values are appropriate. It was further recommended to evaluate the Cantabro, IDT-CT, and APA rut tests to determine acceptable variability and establish precision statements.

State of the Art Review on Prescriptive & Performance Based Approaches for Concrete Durability

Durability has become one of the most important requirements for the concrete structures across the globe. A durable concrete not only leads to the sustainability but serve for longer period without much repair and maintenances for the concrete members. The Concrete in various exposures such as mild, moderate, severe, very severe and extreme conditions was studied by researchers but no significance attention is given for the performance of the concrete in service. In the last few decades, many researchers investigated the causes of structures deterioration and suggested various solutions to tackle the durability issues which are mainly adopting of performance-based specifications rather than prescriptive. In this paper, the previous findings on concrete durability are reviewed. The studies on the durability problems are highlighted along with prescriptive and performance-based approaches and test methods. The effects on service life of the structures along with the solution are reviewed.

Evaluation of Moisture and Decay Models for a New Design Framework for Decay Prediction of Wood

Performance-based, service-life design of wood has been the focus of much research in recent decades. Previous works have been synthesized in various factorized design frameworks presented in the form of technical reports. Factorization does not consider the non-linear dependency between decay-influencing effects, such as between detail design and climate variables. The CLICKdesign project is a joint European effort targeting digital, performance-based specification for service-life design (SLD) of wood. This study evaluates the feasibility of using a semi-empirical moisture model (SMM) as a basis for a digital SLD framework. The performance of the SMM is assessed by comparison against a finite element model (FEM). In addition, two different wood decay models (a logistic, LM, and simplified logistic model (SLM)) are compared. While discrepancies between the SMM and FEM were detected particularly at high wood moisture content, the overall performance of the SMM was deemed sufficient for the application. The main source of uncertainty instead stems from the choice of wood decay model. Based on the results, a new method based on pre-calculated time series, empirical equations, and interpolation is proposed for predicting the service life of wood. The method is fast and simple yet able to deal with non-linear effects between weather variables and the design of details. As such, it can easily be implemented as part of a digital design guideline to provide decision support for architects and engineers, with less uncertainty than existing factorized guidelines.

Comparison of performance-based specification properties for asphalt binders sourced from around the world

This paper documents and discusses performance-based specification properties of 36 asphalt binders. Materials were obtained from commercial sources and purposely distilled from Alberta oil sands crude oils (Athabasca, Cold Lake). Binders were evaluated according to regular Superpave™ specifications, Fraass test, and enhanced protocols based on limiting phase angles and complex moduli. From an overall performance perspective, sol-type binders made from Athabasca and Cold Lake, Alberta and Laguna, Venezuela crudes outperform gel-type ones made from Chinese, Indian, Kuwaiti, Russian, and South Korean sources. Good amounts of asphaltenes together with low wax contents appear to be critical for the production of high quality and durable asphalt binders.

Evaluating Laboratory Tests for Use in Specifications for Unbound Base Course Materials

AbstractA key requirement for performance-based specification for pavement materials is the selection of laboratory tests that can predict their response under conditions similar to those encounter...

Reliability-Based Specification for Asphalt Concrete Pavements

Abstract The use of volumetric-based specifications that utilize air void and asphalt content for the quality control of asphalt pavements is a major concern as there is a lack of fundamental correlation between these mixture properties and long-term pavement performance. In addition to that, the input variabilities’ influence on target reliability and pavement performance is not addressed in these volumetric-based specifications. The aim of this article is to introduce a reliability-based specification for the quality control of top-down cracking in asphalt concrete pavements. The reliability-based specification criteria are developed for two traffic level categories and using design inputs such as hourly equivalent single axle load traffic, asphalt layer thickness, base modulus, and dissipated creep strain energy limit. For the development of the reliability-based specification, several field pavement sections with well-documented performance history and high-quality laboratory and field data were analyzed using the mechanics-based design framework for variability conditions that are representative of actual field conditions. Variation in dissipated creep strain energy limit and asphalt concreter layer thickness has been observed to influence target reliability and overall pavement performance significantly, in comparison with base modulus and hourly equivalent single axle load traffic. The proposed reliability-based specification can complement existing performance-based specifications for the quality control of top-down cracking in asphalt concrete pavements.

Quantifying the freeze-thaw performance of air-entrained concrete using the time to reach critical saturation modelling approach

Many State Highway Agencies have been working to develop performance-based specifications for concrete pavements and concrete bridge decks in freeze-thaw environments. A time to reach critical saturation (TTRCS) model has been proposed to estimate the freeze-thaw performance of concrete. This study evaluates the TTRCS model for thirty different concrete mixtures with varying w/c, air volumes, and quality of air void (size and spacing). Simple quality control test procedures are used to determine the input parameters for the TTRCS model. The estimated time to reach critical saturation is compared with the measured durability factor using ASTM C 666–15. Results indicate that 86% of the mixtures with air volume above 4.5% and a Sequential Air Method (SAM) Number below 0.30 have a normalized time to reach critical saturation of greater than 20, and a durability factor that is greater than 75%. The mixtures with a high range water reducer require a higher volume fraction of entrained air to satisfy the recommended limit for the durability factor. This appears to be due to an interaction between the high range water reducer and air entraining admixture which results in greater air void spacing (i.e., larger air voids). However, the addition of high range water reducer was also found to increase the time to reach critical saturation in the mixtures with a low w/c due to a refined pore structure with a reduction in the connectivity of the matrix pores. Reducing the w/c improves the freeze-thaw performance due to a reduction in the pore volume, connectivity, and absorption rate of the concrete. A relationship is developed to estimate the time to reach critical saturation based on SAM Number and apparent formation factor. In addition, a relationship is proposed to estimate the critical degree of saturation based on air void content and quality.