Concrete Products

MAR 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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Page 50 of 67 March 2019 • 49 TECHNICAL TALK TRB 2019 MEETING TWO-LIFT PLACEMENT AIDS HEAT SYSTEM INSTALLATION Installation of heated pavement systems (HPS)—such as those seen in airfields—is facilitated by two-lift concrete placement, say Hesham Abdualla, Ph.D., Halil Ceylan, Ph.D., Kasthurirangan Gopalakrishnan, Ph.D., Sunghwan Kim, Ph.D., P.E. and Kris- ten Cetin, Ph.D., P.E., Department of Civil, Construction and Environmental Engineering, Iowa State University-Ames; and Peter Taylor, Ph.D., P.E., National Concrete Pavement Tech- nology Center at Iowa State University-Ames, in their 2019 TRB paper, Development of Construction Techniques for Electrically Con- ductive Heated Concrete Pavements. Ice and snow accumulation on paved sur- faces has the potential to reduce pavement surface skid resistance and cause hazardous conditions, the writers observe. "The use of deicing chemical agents or deployment of snow removal equipment to remove snow/ice can cause foreign object damage to aircraft engines, and corrosion to overall airplane structure, leading to undesirable environmen- tal issues," they affirm. "It's also typically costly and time-consuming." HPS represent alternative options for melting ice and snow in airfields, and can be classified into two general categories: hydronic heated-pavement systems (HHPS) and electrically heated pavement systems (EHPS). The former circulate a heated fluid through pipes embedded in the pavement; the latter melt ice and snow using resistive cables embedded in regular concrete or elec- trically-conductive concrete (ECON). Two-lift concrete paving, in which a lower lift can be optimized to enable the use of locally available or recycled materials, while a top lift is optimized for long life and functionality, has become a common con- struction practice in Europe, the Iowa State team notes. Two-lift concrete paving involves either sequential placement of two wet-on- wet layers, or bonding wet to dry layers of concrete, where the bottom layer is thicker than the top layer. Benefits include use of recycled aggregate to achieve cost reduction and production of more sustainable pavements. This method can also provide a high-quality and durable surface, improve skid resistance, and reduced road noise, the authors report. These bene- fits could compensate for the extra labor and trucking costs associated with the require- ments for two slip-form pavers. To this end, systematic design and 3-D visualization of construction procedures were devel- oped to demonstrate the constructability Electrically conductive concrete (ECON) heated pavement system (HPS) at Des Moines Inter- national Airport is constructed (left), and performs during snow event (right). IMAGES: Abdualla, Ceylan, Gopalakrishnan, Kim, Cetin and Taylor Four steps for installing ECON HPS using two-lift concrete paving: upper left, prepare base and place dowel baskets and PVC conduits; upper right, place portland cement concrete layer, or bottom layer, on the prepared base; lower left, place electrodes on the portland cement concrete layer; and, lower right, place ECON layer as top layer over portland cement concrete layer. of ECON-based HPS using two-lift concrete paving. The authors defined four construction steps for constructing the ECON using two- lift concrete paving. The major difference between the construction of ECON using two-lift concrete paving, and typical two-lift concrete paving, is that the ECON is con- structed as a top layer over portland cement concrete (PCC), leaving the bottom layer for electrode installation and wire connections for the system. EI, DIELECTRIC CONSTANT MEASURE CURING ACTION When used with an effectiveness index (EI), the dielectric constant (DC) is a valid means to measure curing membrane performance, say Alireza Joshaghani, Richa Bhardwaj, Dan Zollinger, Ph.D., P.E., Zachry Department of Civil Engineering at Texas A&M University, and Anol Kanti Mukhopadhyay, Texas A&M Transportation Institute, in their TRB paper, Investigating the Effects of Curing Quality on Key Concrete Pavement Surface Properties. "The curing quality of concrete is regarded as one of the principal factors in pavement construction, and often lacks the technol- ogy to qualify it under field conditions," the authors write. "Nonetheless, the application of a curing compound in construction is needed to facilitate the hydration process of the concrete as well as mitigate the moisture loss-induced distress." With PCC performance at stake, the authors wanted to demonstrate viability of identified curing quality indicators. Two indi- cators were defined to evaluate the curing practices related to direct and indirect mea- sures. "The quality of a curing compound and the curing practice to deploy a given compound are considered to be independent

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