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.
Issue link: http://concrete.epubxp.com/i/114208
FEATURE TRB MEETING Additionally, they conclude: • The introduction of nanosilica in concrete results in a workability loss in concrete mix due to high specific surface area of the nanomaterial. However, the target workability of concrete can be maintained by using an appropriate dosage of high-range water reducer. • The loss of air voids from fresh concretes is increased with a higher content of nanosilica. However, the required concrete air content can be achieved by increasing the dosage of air entraining admixture. • Nanosilica increases the compressive strength of concrete. This is due to improved microstructure/pore-structure of concrete. Nanosilica produces nanocrystals of C-S-H, which fills in the micro-pores (chemical effect). Also, the tiny particles of nanosilica fill in the micro-voids and block the pore channels (physical effect). As a result, the concrete microstructure is improved in the presence of nanosilica. • Nanosilica increases the frictional properties of concrete. This can be explained by the increase in contact area, which results from the improved microstructure of concrete through the physical and chemical effects of nanosilica. • The impedance tube absorption test results show that nanosilica can increase sound absorption of concrete material. This is because silica particles increase the vibration dumping capacity of concrete. • It is possible to create the lotus effect on concrete material. In wet condition, the original friction property of concrete pavements can be retained by improving their water repellence through using a coating of nano-lotus leaf. AIR-ENTRAINMENT TARGET VS. FLY ASH CONTENT The amount of the air-entraining agent admixture required to obtain the target air percentage in a concrete mix increases with the increase in the fly ash content in the mix, say Chaitanya Paleti, graduate student, and Jan Olek, professor, School of Civil Engineering, Purdue University, and Tommy E. Nantung, Office of Research and Development, Indiana Department of Transportation, in their paper, Potential Issues with Generation and Stability of Air-Void System due to Incompatibility of Components in Plain and Fly WWW.CONCRETEPRODUCTS.COM CEMENT, FLY ASH PROPERTIES ANALYTE SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K 2O TiO2 P2O5 Mn2O3 SrO Moisture Content Total Alkali Na2Oeq Free CaO L.O.I (950deg) CEMENT (C) 20.59 4.76 1.96 63.77 2.68 3 0.13 0.25 0.35 0.11 0.13 0.03 0.29 1.02 2.61 CLASS F ASH (F) 49.72 25.89 14.13 3.53 1.16 0.69 0.87 2.04 0.24 2.21 3.98 COMPOUNDS (AASHTO M85) 60 C3S 14 C2S 9 C3A 6 C4AF - FINENESS Blaine surface area (m2/kg) 379 Density (g/cc) 3.15 -325 Sieve (%) - 2.44 20.2 SOURCE: Paleti, Olek and Nantung Ash Cementitious Mixtures. Increased use of mineral and chemical admixtures to boost performance of con- crete mixes may result in unexpected incompatibility problems in some mixes, due to complex interactions that freMARCH 2013 | 35