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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48 • March 2019 Materials are the critical component of dura- ble transportation infrastructure, and as such got strong coverage at the 99th annual Trans- portation Research Board meeting earlier this year in Washington, D.C. There, some 12,000 delegates audited presentations in over 800 sessions, which addressed many aspects of transportation design, construction and policy, and encompassed infrastructure built with cast-in-place concrete. Concrete Products was present and offers this report on new research involving cast-in-place concrete for transportation infrastructure. We described TRB 2019 research in prestressed, precast concrete in our February issue (see pages 54-59, "TRB 2019: Nanotechnology Boosts Performance of Cementitious Grouts"). The 100th meeting of TRB will take place January 12–16, 2020. For more information, visit REDUCE CEMENT CONTENT WITH OPTIMIZED GRADATION Optimized aggregate gradation can help reduce quantities of ordinary cement and portland-limestone blended cement in con- crete, say Hung-Wen Chung, Thanachart Subgranon, Chun-Hao Yang, graduate stu- dents, and Mang Tia, professor, University of Florida-Gainesville, and Harvey Deford, struc- tural material research specialist, Florida Department of Transportation, Gainesville, in their peer-reviewed paper, Advantages of Reducing Cement Content for Portland-Lime- stone Cement Pavement Concrete with Optimized Aggregate Gradation. Under ASTM and AASHTO specs, port- land-limestone cement (PLC, Type IL)—a conventional portland cement with between 5 and 15 percent ground limestone by mass— has performance properties comparable to conventional portland cement, but with an inherent improved environmental aspect in that the added powder is not calcined and doesn't produce carbon dioxide emissions as does calcined limestone for cement. "The concrete industry in Florida and the U.S. is presently facing two major challenges, namely the rising cost of cement, and the shortage of fly ash," the authors write. In the meantime, they say, the escalating price of cement, which has increased by 17.8 percent from 2012 to 2015, has caused higher initial costs for structural concrete. They also cite a 2015 forecast of fly ash utilization from the American Road & Transportation Builders Association, projecting demand for fly ash will increase by at least 53 percent through 2035, while production of the material—in concrete and lesser grades—decreased by 30.3 percent from 2008 to 2013. "One of the possible solutions is a more effective design of concrete mixtures in which the cementitious content has been TECHNICAL TALK BY TOM KUENNEN TRB 2019: Reduce portland cement content by optimizing gradation minimized," report Chung, Subgranon, Yang, Deford and Tia. They suggest three approaches to reduce cementitious materials, including minimized cement paste volume in concrete, use of PLC, and optimized aggregates gradation (OAG). The latter is in contrast to a gap-graded mix; its optimized denser gradation is thought to improve air entrainment for a better spac- ing factor, reducing entrapped air voids, and facilitating less shrinkage due to fewer voids needed to be filled with cement paste. The authors' investigations indicate that most Florida DOT concrete mixtures have an excess of paste. "In reality, 5 to 15 percent (by weight) of the cement in most FDOT pavement concrete mixtures can be removed without any adverse effects on the plastic or hardened concrete properties by using these three different approaches," they say. Reduction in cement paste volume using reduced cement content is the direct way, while use of PLC also reduces portland cement content. The OAG method can make concrete denser, more workable and more cohesive, authors observe, adding, "Well-graded aggregate can minimize the cement paste volume, since it makes high aggregate packing density." Their study evaluated the properties of three concrete mix types bearing Type I/II cement; PLC or Type IL cement; or, Type IL cement plus the optimized aggregate gra- dation technique. Chung, Subgranon, Yang, Deford and Tia conclude: • Portland limestone cement (Type IL) con- taining 15 percent limestone powder can be used in Florida as substitute for conventional portland cement (Type I/II) in pavement con- crete with no loss in fresh mix workability, or hardened slab strength and permeability. • The cementitious content of pavement con- crete can be reduced to some extent without loss in mix workability or strength and durability of hardened concrete. When the concrete aggregate gradation is enhanced by the OAG technique, the reduction in cemen- titious content could be increased. The cementitious content of the standard cement (SC) and limestone cement (LC) mixes with no optimized aggregate gradation enhance- ment could be reduced by 10 percent without loss in workability, and could be reduced by 5 percent without loss in strength and dura- bility. For the concrete incorporating OAG, and Type IL cement (OLC) mixes with OAG enhancement, the cementitious content could be reduced by up to 15 percent without loss in workability and by up to 10 percent without loss in strength and durability. • The concrete mixes with OAG enhance- ment (OLC mixes) showed lower modulus of elasticity and lower coefficient of ther- mal expansion, which would result in lower thermal-load induced stresses in concrete pavement slabs and thus potentially better performance. • The concrete mixes with OAG enhancement showed lower drying shrinkage, which would indicate better performance in structural con- crete as well as pavement concrete. "It can be concluded that, from the results of this laboratory study, portland limestone cement can be used in conjunction with [the] OAG technique to reduce the use of ordinary portland cement, and improve the perfor- mance of concrete in pavement application," they conclude. OPTIMIZED AGGREGATE GRADATION Gradation of aggregates used in the concrete mixes evaluated; SC = Standard Concrete using Type I/II cement, LC = Concrete using Type IL cement, and OLC = concrete incor- porating OAG and Type IL cement. TABLE: Chung, Subgranon, Yang, Deford and Tia

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