Synthesis: Accelerating Implementation of Research Findings to Reduce Potential Concrete Pavement Joint Deterioration

Distress has recently been observed in the joints of some concrete pavements, primarily in the wet-freeze states. This distress often begins in longitudinal joints, followed by transverse joints and results in the significant loss of material from the joint area. Although it may only affect approximately 10% of the concrete pavements system-wide, it greatly reduces the service life and increases maintenance costs of the pavements it effects. Primary issues that emerged from studies on this phenomenon include the importance of the timing of joint sawing, the width of the joint opening, degree of concrete or joint sealing, drainage and degree of saturation of the concrete at the joint, quality of the air void system, role of deicing chemicals, quality of curing, and the degree of restraint at the joint. Although this broad collection of issues implies that we still lack complete understanding of all causes of joint deterioration, it also makes it pretty clear that the observed damage is a result of combination of several factors. This study synthesizes completed research related to concrete pavements joint deterioration and provides information to advance the knowledge and understanding of the variables involved in in this deterioration process and suggests the best practices that can lead to its reduction or mitigation

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

Deicing salts are widely used for anti-icing and de-icing operations in pavements. While historically sodium chloride may have been the deicer most commonly used, a wide range of deicing salts have begun to be used to operate at lower temperatures, to stick to the road better and to improve other aspects of performance such as environmental impact or corrosion resistance. It has been observed that some chloride based deicing salts can react with the calcium hydroxide in the mixture resulting in the formation of calcium oxychloride an expansive phase that can damage concrete pavements, especially at the joints. This report describes the two main objectives of this work. First, the report documents the development a standardized approach to use low temperature differential scanning calorimetry (LT-DSC) to assess the influence of cementitious binder composition on the potential for calcium oxychloride formation. Second, this work will assess the influence of blended salt cocktails on the formation of calcium oxychloride

Influence of Activation Parameters on the Mechanical and Microstructure Properties of an Alkali-Activated BOF Steel Slag

ABSTRACT: Steel slag (SS) is a secondary material from steelmaking production with little commercial value. Its volumetric expansion and low reactivity limit the use of SS in Portland cement (PC)- based materials. This study investigated the potential use of basic oxygen furnace (BOF) slag as a single precursor in alkali-activated matrices (AAMs). Six AAM pastes were assessed by changing the silica modulus (0.75, 1.50 and 2.22) and the sodium concentration (4% or 6% Na2O?wt. SS). The early hydration was assessed using isothermal calorimetry (IC), followed by the assessment of the mechanical performance (compressive strength), apparent porosity, and structure and microstructure characterization (X-ray diffraction, thermogravimetric analysis and scanning electron microscopy). The results indicated that although the BOF slag may be considered a low-reactivity material, the alkaline environment effectively dissolved important crystalline phases to produce hydrates (reaction products). An optimized combination of activator sources was achieved with 4% Na2O and a silica modulus of 1.50?2.22, with a compressive strength up to 20 MPa, a significant amount of reaction products (C-S-H/C-A-S-H gels), and low initial and cumulative heat release. Those properties will help to promote SS recycling use in future engineering projects that do not require high-strength materials.This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—finance code 001, grant PPM-00709-18 (FAPEMIG) and grant 316882/2021-6 (CNPq

Ultrasonic wave reflection measurements on self-compacting pastes and concretes

The objective of this study was to extend the use of combined longitudinal (P-wave) and shear (S-wave) ultrasonic wave reflection (UWR) to monitor the setting and stiffening of self-compacting pastes and concretes. An additional objective was to interpret the UWR responses of various modified cement pastes. A polymeric buffer with acoustic impedance close to that of cement paste, high impact polystyrene, was chosen to obtain sensitive results from the early hydration period. Criteria for initial and final set developed by our group in a prior study were used to compute setting times by UWR. UWR results were compared with standard penetration measurements. Stiffening behavior and setting times for normal cement pastes, pastes modified with mineral and chemical admixtures, self-compacting pastes, and concretes were explored using penetration resistance, S-wave and P-wave reflection. All three methods showed that set times of pastes varied linearly with w/c, that superplasticizer and fly ash delayed the set times of pastes, and that differences in w/cm, sp/cm, and fa/cm could be detected. Final set times determined from UWR correlated well with those from penetration resistance. Initial set times from S-wave reflection did not correlate very well with those from penetration resistance. Final set times from P-wave and S-wave reflection were roughly the same. Pastes with different chemical admixtures were tested, and the effects of these admixtures on stiffening were determined using UWR. Self-compacting concretes were studied using UWR, and their response and setting times were largely similar to that of corresponding self-compacting pastes. The P-wave reflection response was explored in detail, and the phenomenon of partial debonding and the factors affecting it were explained. Partial debonding is probably caused by autogenous shrinkage at final set, and was controlled and limited by water. The extent of partial debonding was higher with the transducers placed on the side as opposed to the bottom, and the S-wave transducer seemed to promote debonding in the P-wave reflection, whereas the P-wave transducer seemed to reduce debonding in the S-wave reflection. Simultaneous formwork pressure testing and UWR were performed; however, no clear correlation was seen between the two properties

Supplementary Cementitious Materials Reactivity: From Model Systems to Concrete

Newly developed reactivity tests for supplementary cementitious materials have shown the ability to quantify reactivity and to differentiate reactive and inert materials. Recent results using the modified R3 test are summarized here. The test uses a model system of supplementary cementitious materials mixed with calcium hydroxide in a simulated pore solution at 50 ℃. Heat release and calcium hydroxide consumption of the supplementary cementitious materials are measured. The reactivity of a large number of conventional and alternative materials has been measured using this test. By using both heat release and calcium hydroxide consumption, two measures of reactivity are obtained, and the test is able to differentiate pozzolanic, latent hydraulic, and inert materials. While the measured reactivity correlates with the properties of cementitious pastes, other factors including the supplementary cementitious material replacement level and the age of testing also influence these predictions. Thoughts on the use of reactivity testing to predict concrete durability are presented

Recent developments in reactivity testing of supplementary cementitious materials

Identification and rapid characterization of novel supplementary cementitious materials (SCMs) is a critical need, driven by shortfalls in conventional SCMs. In this study, we present a discussion of recently developed reactivity tests – the R3 test, the modified R3 test, the lime strength test, and the bulk resistivity index test. These tests measure reactivity parameters such as heat release, bound water, calcium hydroxide consumption, strength, and bulk resistivity. All tests can screen inert from reactive materials. To additionally differentiate pozzolanic and latent hydraulic materials, two parameters, for example, calcium hydroxide consumption and heat release, are needed. The influences of SCM bulk chemistry, amorphous content, and fineness on measured reactivity are outlined. Reactivity test outputs can predict strength and durability of cement paste/mortar/concrete; however, caution must be exercised as these properties are influenced by a variety of other factors independent of reactivity. Thoughts are provided on using reactivity tests to screen materials for concrete durability

Extending fly ash and pumice usage through blending with inert basaltic fines

Massive amounts of quarry fines are available worldwide. These materials are generally inert, thus limiting their applications. At the same time, shortfalls in conventional supplementary cementitious materials (SCMs) have become an increasing challenge. We can extend SCM usage and reduce filler landfilling by blending these materials together. This paper investigated the proportions of fly ash and pumice that could be replaced with inert basaltic fines without degrading properties significantly. Blended SCM reactivity, and cement paste compressive strength, bulk resistivity, and calcium hydroxide content over 91 days, and alkali-silica reaction mitigation in mortars were investigated. No/minimal synergistic effects between basaltic fines and fly ash or pumice were found. Thus, by measuring initial reactivity or bulk resistivity of end members, an estimate of reactivity, resistivity, and the effects of the blended SCMs on concrete can be established. Replacement of fly ash or pumice by inert materials is likely limited to 40%, depending on the specific applications