Tim Barrett

Relating Compressive Strength to Heat Release in Mortars

Conventionally, isothermal calorimetry and ASTM C186 heat of hydration results are reported on the basis of heat per mass of cement (powder), with typical units being Joules per gram (of cement), for example. Given that it is the filling of porosity with hydration products that is chiefly responsible for strength development in cement-based materials, there might be merit in instead reporting these results in terms of the unit volume of (initial) water. This paper examines a database of well over 200 mortar mixtures to investigate the relationship between heat release and mortar cube compressive strength development. For reasonably low water-to-cementitious-materials ratios (w/cm) (w/cm

Reducing Joint Damage in Concrete Pavements: Quantifying Calcium Oxychloride Formation

Deterioration has been observed at the joints of many portland cement–based concrete pavements in midwestern U.S. states. It has been shown that this damage can be caused by either classic freeze–thaw behavior triggered by high saturation levels or a chemical reaction that occurs between the deicing salt (in this study, calcium chloride) and the cementitious matrix. The objective of this study was to show that low-temperature differential scanning calorimetry could be used to quantify the potential for the chemical reaction between the salt and matrix (i.e., calcium oxychloride formation). The formation of calcium oxychloride is expansive and may lead to significant cracking and spalling without exposure to freeze–thaw cycles. This study examined pastes made with ordinary portland cement; portland limestone cement; and portland cement combined with fly ash, slag, or silica fume. The results indicate that the amount of calcium oxychloride formation that occurs is not significantly different between ordinary portland cements and portland limestone cements. The addition of supplementary cementitious materials reduces the formation of the calcium oxychloride, presumably because of the reduction of calcium hydroxide from dilution, the pozzolanic reaction, and a reduction in the alkali content in the pore solution. The results also indicate that sealers can be used to create a barrier between the salt and the calcium hydroxide or that they can react with the calcium hydroxide, thereby reducing the amount of calcium oxychloride.

Determining the Moisture Content of Pre-Wetted Lightweight Aggregate: Assessing the Variability of the Paper Towel and Centrifuge Methods

Internally cured (IC) concrete is frequently produced in North America using pre-wetted lightweight aggregate (LWA). One important aspect associated with the production of quality IC concrete is the accurate determination of the moisture content, including absorbed moisture and surface moisture of the LWA. Knowledge of the moisture content enables aggregate moisture corrections to be made for the concrete mixture, thereby enabling an accurate water-to-cement ratio to be maintained. Two methods for determining the moisture content of LWA include the specified ASTM C1761-13b “paper towel method” and a method that uses a centrifuge (Miller, Barrett, Zander, & Weiss, 2014). There are limited data available on the variability associated with either of these approaches when the test is performed by multiple users. In this study, the absorption of four commercially available LWAs was tested by a single operator in a single laboratory using the centrifuge method. In addition, the absorption of three commercially available LWAs was tested by 25 users performing both experimental methods. This article provides an estimation of precision associated with both a single operator and multiple operators performing both the paper towel method and the centrifuge method to find the absorption of pre-wetted lightweight fine aggregate.

Performance of Portland Limestone Cements

Portland limestone cements (PLCs) have recently been approved as a part of the ASTM C595/AASHTO M240 specifications. These cements are designed to enable more sustainable concrete production by replacing up to 15% of the clinker with interground limestone particles. The PLCs represent a potential method to reduce the carbon dioxide embodied in built infrastructure and extend the life of limestone quarries. This paper presents a comparison of the performance of three commercially available PLCs meeting the ASTM C595/AASHTO M240 specifications and three ordinary portland cements (OPCs) made from the same cement clinkers. An additional OPC was blended with limestone that had two mean particle sizes. One OPC and PLC were used with a Class C fly ash. Each of these cementitious systems was used to produce typical concrete paving mixtures with the performance of these materials being quantified through a series of standardized tests. The results of the study show that the mechanical properties of PLCs have negligible changes as they relate to design practices and implementation. The early-age volume changes of a PLC ground to levels consistent with achieving similar 28-day strengths were shown to be similar to that of the corresponding OPC, whereas PLCs that were ground significantly finer might lead to increased early-age shrinkage. The transport properties show behavior that is ±30% of the conventional OPC, whereas the results for PLC systems containing fly ash show a synergistic effect with improved performance. The overall results of this study show that PLCs conforming to ASTM C595/AASHTO M240 could achieve similar performance as the OPC they would replace.

Using a Centrifuge to Determine Moisture Properties of Lightweight Fine Aggregate for Use in Internal Curing

Internally cured (IC) concrete is frequently produced using pre-wetted lightweight aggregate (LWA). One important aspect associated with preparing quality IC concrete is being able to determine the absorbed moisture and surface moisture associated with the LWA which enables aggregate moisture corrections to be made for the concrete mixture. ASTM 1761-13b specifies the use of the “paper towel method” to define a surface dry state for pre-wetted LWA; however, this can be time consuming and hard to perform at the batching plant. This paper proposes an alternative method for obtaining a surface dry state of the aggregate based on spinning the pre-wetted LWA in a centrifuge. It is shown that using a centrifuge (with bowl radius of 11.4 cm) for 3 min at 2000 rpm permits a surface dry state to be obtained consistently which enables surface and absorbed moisture to be determined accurately and rapidly. The moisture values obtained using the centrifuge correspond well with those obtained using the paper towel method.

Assessing a concrete's resistance to chloride ion ingress using the formation factor

Abstract Concrete in service environments is often exposed to chloride ions which can accelerate the degradation process by causing corrosion of the reinforcing steel. Resistivity measurements have been gaining interest as a method to assess concrete quality. This chapter will discuss why the formation factor, a quantifiable material property that describes the pore network and its connectivity, is the preferred method to assess concrete quality. The chapter discusses how the formation factor can be easily calculated by using an electrical measurements and knowledge of the pore solution properties and how the measured formation factor can be used as an estimation of service life.

Documentation of the INDOT Experience and Construction of the Bridge Decks Containing Internal Curing in 2013

The Indiana Department of Transportation (INDOT) constructed four bridge decks utilizing internally cured, high performance concrete (IC HPC) during the summer of 2013. These decks implement research findings from the research presented in the FHWA/IN/JTRP‐2010/10 report where internal curing was proposed as one method to reduce the potential for shrinkage cracking, leading to improved durability. The objective of this research was to document the construction of the four IC HPC bridge decks that were constructed in Indiana during 2013 and quantify the properties and performance of these decks. This report contains documentation of the production and construction of IC HPC concrete for the four bridge decks in this study. In addition, samples of the IC HPC used in construction were compared with a reference high performance concrete (HPC) which did not utilize internal curing. These samples were transported to the laboratory where the mechanical properties, resistance to chloride migration, and potential for shrinkage and cracking was assessed. Using experimental results and mixture proportions, the diffusion based service life of the bridge decks was able to be estimated. Collectively, the results indicate that the IC HPC mixtures that were produced as a part of this study exhibit the potential to more than triple the service life of the typical bridge deck in Indiana while reducing the early age autogenous shrinkage by more than 80% compared to non‐internally cured concretes.

Performance of Concrete Pavement in the Presence of Deicing Salts and Deicing Salt Cocktails

• Some concrete pavements have shown premature deterioration at the joints. It has been proposed that this can be attributed to two primary factors: increased fl uid saturation and a chemical reaction that occurs between deicing salts and the cement matrix. • A test method was developed/formalized that uses a low temperature diff erential scanning calorimeter (LTDSC) test method to quantify the chemical reaction that occurs between the cementitious matrix and the deicing salt to form calcium oxychloride. • It is proposed that the LTDSC test be used to qualify the potential for calcium oxychloride formation in a cementitious matrix. Currently two primary JOINT TRANSPORTATION RESEARCH PROGRAM

Removing obstacles for pavement cost reduction by examining early age opening requirements : material properties.

The risk of cracking in a concrete pavement that is opened to traffic at early ages is related to the maximum tensile stress that develops in the pavement and its relationship to the measured, age dependent, flexural strength of a beam. The stress that develops in the pavement is due to several factors including traffic loading and restrained volume change caused by thermal or hygral variations. The stress that develops is also dependent on the time-dependent mechanical properties, pavement thickness, and subgrade stiffness. There is a strong incentive to open many pavements to traffic as early as possible to allow construction traffic or traffic from the traveling public to use the pavement. However, if the pavement is opened to traffic too early, cracking may occur that may compromise the service life of the pavement. The purpose of this report is two-fold: 1) to examine the current opening strength requirements for concrete pavements (typically a flexural strength from beams, and 2) to propose a criterion based on the time-dependent changes of ratio of the tensile stress to the flexural strength, which accounts for pavement thickness and subgrade stiffness without adding unnecessary risk for premature cracking. An Accelerated Pavement Testing, APT, facility was used to test concrete pavements that are opened to traffic at an early age to provide data that can be compared with an analytical model to determine the effective ratio of the tensile stress to the flexural strength based on the relevant features of the concrete pavement, the subgrade, and the traffic load. It is anticipated that this type of opening criteria can help the decision makers in two ways: 1) it can open pavement sections earlier thereby reducing construction time and 2) it may help to minimize the use of materials with overly accelerated strength gain that are suspected to be more susceptible to develop damage at early ages than materials that gain strength more slowly.

Increased Use of Fly Ash in Hydraulic Cement Concrete (HCC) for Pavement Layers and Transportation Structures

Fly ash is commonly used as a supplementary cementitious material (SCM) in the production of portland cement concrete. Concrete produced with high fly ash replacement levels is considered high volume fly ash (HVFA) concrete. HVFA concrete has many benefits, including reduced concrete production cost, reduced greenhouse gas emissions, and improved sustainability. Despite the advantages, there are several barriers that limit the use of HVFA concrete. One of the main limitations to the increased usage of HVFA concrete is the lack of contractor and transportation agency familiarity with the setting time and strength development of these concrete mixtures. For this research, a laboratory-testing program was developed to examine the effect of fly ash type, fly ash dosage, cement chemical composition, and environmental conditions on the hydration development, setting times, and compressive strength development of HVFA concrete. Results from semi-adiabatic calorimetry were used to develop a hydration model for HVFA concrete. Finally, the ConcreteWorks software program was used to predict the in-place performance of selected HVFA concrete mixtures when placed in various transportation structures. It is concluded that HVFA concrete may be produced to have comparable setting times and earlyage compressive strength development to conventional portland cement concrete when used for transportation infrastructure.