Two-lift concrete paving (2LCP) involves placing two layers of concrete (wet-on-wet) instead of a single homogeneous layer. The practice not only allows the use of local aggregates that might not be suitable for conventional concrete pavement but also provides opportunities for incorporating recycled materials and higher levels of supplemental cementitious materials to produce an economical and sustainable pavement. More importantly, the practice can also produce more durable concrete pavements for either airfield or highway applications through the optimization of top lift mixture design, as well as with desirable surface characteristics including improved skid resistance and reduced noise. The presentation discussed the potential technical benefits of 2LCP. While 2LCP is likely to result in increased construction costs associated with additional equipment, labor, and scheduling effort, potential savings from the use of lower-quality, less expensive concrete and aggregate in the bottom lift could be sufficient to offset the additional costs. According to cost information collected from recently constructed 2LCP projects in the United States, a case-based cost analysis was also performed to evaluate the cost-effectiveness of the 2LCP practice. Through information collected from an extensive literature review, surveys, and interviews, a summary of the benefits of 2LCP from technical and cost-effectiveness perspectives was provided to justify the implementation of the 2LCP concept.

Two-lift concrete pavement, sometimes referred to as composite pavement, is an innovative technique that involves placing a thinner portland concrete layer over a thicker portland concrete layer at a specified interval.A shortage of suitable aggregates for use in concrete pavements in some regions of the world has become a very serious concern for some organizations.Importing aggregates from faraway locations is neither economical nor practical/sustainable; therefore, the use of local materials is highly desirable.The strength of two-lift concrete pavement technology lies in being able to utilize any of the following for the bottom lift: locally available aggregates, manufactured sands, highcoefficient of thermal expansion (CoTE) aggregates, recycled concrete aggregates (RCA), fractionated reclaimed asphalt pavements (FRAP), lower cement content, or a higher amount of supplementary cementitious materials (SCMs).Some of these materials, however, may not be allowed to be used in single-lift concrete pavements due to issues related to polishing, durability, or strength gain.This paper gives a thorough overview of the historical background, potential environmental and sustainable advantages, and practical challenges related to two-lift pavement.

Polymer-impregnated concrete (PIC) was developed in the 1970s by Brookhaven National Laboratory and the Bureau of Reclamation. Fully impregnated concrete had excellent strength and durability properties. Partially impregnated concrete had very good resistance to water and chloride penetration and to abrasion. Neither of these processes is used to any significant degree. The reasons for the lack of use and the potential for future use are discussed including potential applications to make use of the very good material properties that are possible.

Concrete-polymer materials (CPMs) include polymer-impregnated concrete (PIC), polymer concrete (PC), and polymer-modified concrete (PMC) along with sulfur concrete and crack-filling resins and monomers. These materials began to be developed in the 1950s, but it was not until the early 1970s that they began to be well known in the industry. PIC is no longer being used, but PC and PMC are widely used as are the crack-filling monomers. The materials have come a long way in the nearly 50 years after they became known. Many conferences and workshops have been held, hundreds of papers have been published, and the American Concrete Institute Committee 548 has produced many special publications, guides, and specifications for the use of the materials. The future is bright. New polymers are coming on stream that offer many potential benefits for CPM. Nanotechnology will likely play an important role. Many innovative applications and processes to use CPC including 3D printing and new and exciting products using precast PC are on the horizon.

Polymer concrete (PC) overlays have been successfully used since the 1970s primarily by transportation agencies on bridges. Polymers used for overlays have seen significant improvements, and the current overlays have proven to be durable, skid resistant, and cost-effective. Over 2400 overlays had been installed by 2009, and overlays are a standard bridge protection system by departments of transportation based on an extensive survey of US and Canadian provinces. Slurry, multiple-layer, and premixed overlays are the most widely used. Epoxies are the most widely used resins. Many states have published specifications on the construction of overlays.

Thermomechanical response of coefficient of thermal expansion (CTE) test samples plays an important role in the consistency of CTE test results. Saturated concrete samples while subjected to heating and cooling develop internal pressure due to the dissimilar thermal expansion/contraction of solid and liquid phases. This fundamental property of saturated concrete has not yet been considered as a criterion to improve the CTE test procedure. This paper presents an experimental investigation to reduce the effect of internal water pressure on the measured CTE results. The paper experimentally evaluates three techniques-preconditioning the concrete samples by heating and cooling cycles prior to CTE test, precracking concrete samples, and reducing the rate of temperature change. Preconditioning concrete samples by heating and cooling cycles prior to CTE testing noticeably improves the consistency of CTE test results. Decreasing the rate of temperature change also improves the consistency of the test results but significantly increases the test duration. Precracking shows improvement in a few test parameters, but the results are unreliable for in situ concrete due to the adverse effect of increased porosity. (C) 2017 American Society of Civil Engineers.

Coefficient of thermal expansion (CTE) test procedures use saturated concrete samples to (ostensibly) avoid the effect of moisture content. Concrete is a porous material, and internal water pressure develops in saturated concrete when subjected to temperature change due to the difference in CTE between liquid and solid phases. The measured CTE is affected by the internal water pressure development in saturated concrete samples. This paper represents an analytical model that was developed based on the poromechanical phenomenon of concrete to determine the time dependent internal water pressure and axial strain development. Material properties including, CTE, moduli of liquid and solid phase of concrete, as well as porosity and permeability of concrete samples have influence on the internal water pressure development. The predicted axial strain from the proposed numerical model for saturated concrete samples subjected to temperature changes were consistent with the experimental results. Predicted internal water pressure of the hardened concrete cylinder was as high as 700 psi (4.8 MPa), which is sufficiently high to potentially induce microcracking. (C) 2016 Elsevier Ltd. All rights reserved.

•First systematic approach to optimize concrete CTE.•CTE can be reduced by replacing high-CTE aggregates with low-CTE aggregates.•CTE can be reduced by reducing cement paste volume.•A step-by-step concrete CTE optimization technique.

Polymer concrete (PC) overlays have proven to be a very effective method of extending the lives of bridge decks and improving skid resistance. Many states in the U.S have specifications and have used overlays on hundreds of bridge decks. Multiple-layer epoxy, epoxy and methacrylate slurry, and polyester premixed overlays have been widely used. One of the keys to successful performance is surface preparation. The very light weight, water tightness, good skid resistance, excellent bond to concrete, and excellent durability have made PC overlays a very sustainable solution for increasing the life of bridges and parking garages, But in recent years very thin overlays referred to as high-friction surface treatments (HFST) have been widely used to provide skid resistance for asphalt pavements in high accident zones, particularly on horizontal curves. Several state departments of transportation (DOTs) have reported very significant reductions in accidents after HFST have been applied. The total length of the application is often only a few hundred meters or less. The cost, when compared to other remedial measures, has been very competitive. The treatments are very similar to very thin slurry overlays. The purpose is not to structurally rehabilitate the pavement, but to provide increased skid resistance for safety. There is also an increased use of thin overlays to provide color for applications including pedestrian and bicycle lanes, bus lanes, entrance and exit ramps, cross walks, and rail road crossings. There are few standards in the U.S. for colors in various applications or for where color should be used. But these thin overlays provide high visibility, skid resistance, and long life. A discussion of these applications, materials and installation methods, and where available, costs, will be presented.

A study was conducted to evaluate the effect of coefficient of thermal expansion (CTE) test procedures and length-change measuring devices on the measured CTE values. Twenty different coarse aggregate sources were tested using the Texas Department of Transportation (TxDOT) and the American Association of State Highway and Transportation Officials (AASHTO) suggested CTE methods. Two different types of length-change measuring devices, linear variable differential transformers (LVDTs) and differential variable reluctance transducers (DVRTs), were used. No significant effects of length-change measuring devices were observed on the CTE values measured by the TxDOT method. However, the test methods have shown effects on the measured values. The TxDOT method yields higher CTE values than the AASHTO method. Data obtained in this study confirmed that the internal water pressure development during the heating and cooling cycles is one of the potential reasons. Internal water pressure can significantly affect the CTE of concrete. Further investigation is needed to determine the effect of internal water pressure on the CTE, which affects the design and service life of concrete pavements. (C) 2014 American Society of Civil Engineers.

Sustainability is important in all engineering decisions. Every technical organization now has the objective to promote sustainability. Polymer concrete (PC), in order to have a rightful place in industry, must be sustainable. Based on several criteria, it can be shown that PC materials and products are sustainable. PC applications to be discussed include repair, concrete overlays, and precast products. When designed and constructed appropriately, PC materials and products are sustainable.

Pavement concrete containing aggregates that do not meet ASTM C33 often experiences workability problems. One of the reasons is the lack of proper guidelines for proportioning concrete that contains aggregates with poor shape, texture, and grading. Commonly used methods, such as ACI 211, were developed for aggregates that meet ASTM C33; these methods are not adequate for optimizing mixtures containing aggregates such as manufactured sands. This paper presents a simple mixture proportioning method for designing pavement concrete with low slump. The proposed method has the potential to minimize the cement content of paving mixtures with any available source or combination of aggregate without affecting performance. Several combinations of aggregates were tested and the results for slump, compressive strength, and modulus of elasticity are presented in this paper.

Current Texas Department of Transportation (TxDOT) procedures for evaluating coarse aggregate for portland cement concrete (PCC) have been in place for over 39 years. Item 421 in the TxDOT “Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges” describes the tests and test limits that must be met by aggregates before they can be approved for use in portland cement concrete applications. The intention of Item 421 is to ensure that only strong, durable aggregates are used in concrete so that the life of concrete is not cut short by common distress mechanisms, which ultimately lead to costly repairs and replacements. The two main tests currently used by TxDOT to evaluate aggregates are the magnesium sulfate soundness test and the Los Angeles abrasion and impact test. Unfortunately, past research has shown that the magnesium sulfate soundness test and the Los Angeles abrasion and impact test are not able to successfully predict the field performance of an aggregate in concrete. The requirements of Item 421 have thus far done a reasonably good job of ensuring long-lasting concrete; however, the current tests and test limits may be unnecessarily precluding the use of some local materials. As high quality aggregate sources are depleted and transportation costs increase, it will become more necessary to distinguish good performers from marginal and poor performers in the future. If aggregate tests can be found that demonstrate better correlations with field performance, it may be possible to use more local aggregate sources and still provide the desired level of reliability for pavements, bridges, and other TxDOT concrete applications. Researchers will attempt to relate this test data to concrete behavior and ultimately recommend tests for improved TxDOT aggregate specifications.

Two-lift concrete paving (2LCP) involves placing two layers of concrete (wet-on-wet) instead of a single homogeneous layer, as typically done in the United States. 2LCP offers the opportunity to optimize the use of local aggregates, recycled materials to produce an economical, durable, and sustainable pavement system with the most desirable surface characteristics (improved skid resistance and reduced noise). Districts including Houston, Fort Worth, and Dallas have the potential to receive great benefit from the concept by being able to use more local materials that is not considered appropriate for traditional (single-lift) concrete pavement used. Despite above mentioned benefits, challenges of 2LCP are to have the proper paving equipment, pavement construction management, the right mixture proportions to use the local materials in the bottom lift, which results in an economical pavement placement, and the proper proportions and materials to ensure adequate surface friction and abrasion resistance in the top lift. A comprehensive literature review was conducted to gather previous experiences and past performance of 2LCP, particularly to justify the cost and efficiently execute the process of 2LCP. Surveys and interviews were conducted on contractors and agencies with experience with 2LCP. A one-day workshop regarding 2LCP was organized to obtain information from a wide range of agency, construction, equipment manufacturer, and Texas Department of Transportation (TxDOT) personnel with experience and interest in 2LCP. The workshop also served as a solicitation of ideas of best practice, most cost effective approach, concerns, and requirements associated with materials and construction of 2LCP. This report discusses additional requirements in materials, equipment and construction, project scheduling, and jobsite management that will be beneficial in the implementation of 2LCP construction. This study also evaluated feasibility and cost effectiveness of 2LCP, particularly in Texas.

Thermal stress development in concrete structures is significantly influenced by the coefficient of thermal expansion (CTE) of concrete. Optimizing concrete CTE can reduce the thermal stress, which will eventually reduce the cracking potential of concrete structures. At early age, when concrete has low strength, it is much more vulnerable to cracking. Early-age cracking has a detrimental effect on the durability of concrete structures. This study presents the importance of concrete CTE on the thermal stress development in concrete structures as well as three techniques to reduce the CTE of concrete. Replacing high CTE coarse aggregates with low CTE coarse aggregates is the most effective method for reducing concrete CTE. Concrete CTE can also be reduced by reducing cement paste volume. However, if the cement paste reduction increases the void content in the concrete system, saturated concrete CTE is likely to increase.

Two-lift concrete paving (2LCP) involves placing two layers of concrete (wet-on-wet) instead of a single homogeneous layer. The practice not only allows the use of local aggregates that might not be suitable for conventional pavement, but also provides opportunities for incorporating recycled materials and higher levels of supplemental cementitious materials (SCMs) to produce an economical and sustainable pavement. The practice can also produce durable pavements through the optimization of top lift mixture design with desirable surface characteristics including improved skid resistance and reduced noise. While 2LCP could become a viable and competitive alternative to conventional single-lift paving, challenges of 2LCP are to have the proper paving equipment and pavement construction management, the right mixture proportions to ensure the use of local materials in the bottom lift to result in an economical placement and to ensure a high quality top lift. Through information collected from an extensive literature review, surveys, interviews and a recently hosted 2LCP workshop, a summary of benefits of 2LCP from sustainability and cost effectiveness perspectives was provided. Four 2LCP projects recently constructed in the U.S. were summarized as case studies. This paper also discusses additional requirements in materials, equipment and construction, project scheduling and jobsite management, which will be beneficial in the implementation of 2LCP construction.

The coefficient of thermal expansion (COTE) is an important concrete property that characterizes the dimensional change of concrete subjected to temperature change. In jointed concrete pavements (JCP), expansion joints are used to accommodate length changes due to temperature variations. However, for continuously reinforced concrete pavements (CRCP) with high COTE aggregates, there are no expansion joints to accommodate the length changes. In Texas some districts with high volumes of CRCP, such as Houston, Dallas, and Forth Worth, experience a high degree of transverse cracking, horizontal cracking, and punchouts due to the environmental loading in high COTE concrete CRCP. Very recently the Texas Department of Transportation (TxDOT) imposed a limit on COTE as an acceptance criterion for pavement concrete aggregates. Houston and Beaumont do not have low COTE aggregate sources in the vicinity, and to meet the current TxDOT requirement these two districts have to haul aggregates from long distances. This will not only increase the transportation cost but also limit the use of locally available good quality aggregates, which has high COTE. COTE of concrete can be reduced by blending high and low COTE aggregates. This research study used three high COTE aggregate sources from different strategic locations in Texas suggested by TxDOT; they were each blended with low COTE limestone aggregate at different replacement ratios. Results showed that concrete COTE can be reduced by blending low COTE aggregates with high COTE aggregates. The COTE of concrete decreases linearly with an increase in limestone replacement. These findings will help TxDOT use the local high COTE aggregate sources by blending with imported low COTE aggregates. Aggregate producers with high COTE aggregates can also determine the degree of replacement necessary for their aggregates to be accepted in a TxDOT CRCP paving projects.

Fly ash is frequently used to replace cement in concrete, but it is difficult to predict performance based only on the oxide composition, which is typically the only compositional information available. In order to better utilize fly ash in concrete, it is important to develop more meaningful characterization methods and correlate these with performance. The research presented here uses a combination of analytical methods, including X-ray powder diffraction, scanning electron microscopy coupled with multispectral image analysis, and solution analysis to determine the compositions of the glassy phases in a specific fly ash and to examine the fly ash's reactivity in late- and early-age cement pore solutions, ultrapure water, and sodium hydroxide. The dissolution of individual glassy phases in the fly ash was tracked over time and the precipitation of reaction products monitored. A high-calcium aluminosilicate glass was the most reactive, a low-calcium aluminosilicate glass was of intermediate reactivity and a medium-calcium aluminosilicate glass had the lowest reactivity in the solutions tested for a specific fly ash. This result suggests the glass composition has a strong effect on reactivity, but that that there is not a strict correlation between calcium content and glass reactivity.

Manufactured fine aggregates are a product created when rocks are crushed using a mechanical crusher. With the depletion of sources of natural sands, the usage of manufactured fine aggregates has increased. Manufactured fine aggregates have properties that differ from natural sands; for this reason, the plastic and hardened properties of concrete produced using manufactured fine aggregates differ from the properties of concrete made with natural sands. The main concrete properties affected by the usage of manufactured fine aggregates are skid resistance, workability, and finishability. The aim of this research project was to investigate how manufactured fine aggregates could be used in concrete pavements without causing workability or skid related issues. To improve the workability of concrete made with manufactured fine aggregates, the use of the optimized mixture proportioning method developed by the International Center for Aggregate Research (ICAR) was investigated. Results obtained from this testing were used to make recommendations on how to optimize class P concrete mixtures made with any type and combination of aggregates.