Electrical Resistivity Measurement Method for Measuring Water Absorption Characterizes Properties of Recycled Concrete Fine Particles
by Jihwan Kim, Goangseup Zi, and David A. Lange
ACI Materials Journal November/December 2017
Newswise — An electrical resistivity method for measuring water absorption of very fine particles makes it easier to characterize stock materials that are recyclable in construction applications. Better methods for characterizing the properties of recycled concrete fine particles are necessary to further advance their acceptance in construction practice. With the growing emphasis on sustainability, construction materials can be a viable solution for construction and demolition waste.
Measuring Gravity and Water Absorption
The very fine particles produced when crushing concrete for recycling purposes are notoriously difficult to characterize and routinely discarded into landfills (Fig. 1). The fine particles as fine aggregate in mixtures should be characterized by density and water absorption to facilitate mixture design.
As with any fine aggregate, the specific gravity and water absorption of recycled fine particles should be measured to facilitate mixture design and quality control of fresh and hardened concrete. To do so, the saturated surface-dry (SSD) state must be defined so that the total water content of the materials can be controlled, and the correct batch weights determined. Saturated surface-dry is defined as the condition of aggregates in which all pores are filled with water, but with no film of water on the surface. The SSD condition of fine aggregates can be determined using ASTM C128 specifications. Using standard methods for recycled fines, however, leads to inaccurate determination of the specific gravity and absorption values, thus degrading the quality of construction materials made with recycled aggregate.
Testing the Electrical Resistivity of Fines
For the test studies presented here, the electrical resistivity of fines was used to indicate water content. The resistivity measurements, as a function of water contents, were carried out to determine the SSD condition of recycled concrete, limestone, and natural sand fines retained on No. 100 (150 μm (0.0059 in.)) and No. 200 (75 μm (0.0030 in.)) sieves. Test results were analyzed using the percolation theory to interpret the correct value for the SSD condition. The water absorption, or water content in SSD state, of different fines were presented and discussed. The effects of mold shape (cylinder and prism) and resistivity measurement method (two-probe (2p) and four-probe (4p) methods) on the absorption values of fines were evaluated (Fig. 2). Additionally, the absorption obtained from the resistivity measurements was compared with that measured from standard test methods.
The results described in this work showed the electrical resistivity measurement method has the potential to be an accurate means for measuring the water absorption of very fine particles. Such advances in characterization methods for fine particles support the broader acceptance of recycled concrete.
The research can be found in a paper titled “Measurement of Water Absorption of Very Fine Particles Using Electrical Resistivity,” published by ACI Materials Journal November/December 2017.
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