The strain sensitivity of brass fiber reinforced concrete

The structures are challenged by earthquakes and other environmental factors. Structural health monitoring is crucial to protect the lives. The strain gages used in structural health monitoring have low durability and can get point wise measurements which limit their use. In this study, five different concrete mixtures with different brass fiber volume fractions were designed. Along with the control mixture which does not have brass fiber, six mixtures were designed and three cube samples from each mixture were cast and cured. Compression test was conducted with simultaneous measurement of electrical resistance. The brass fiber reinforced concrete has strong linear relationship between the electrical resistance change and strain. Important progress was achieved in development of “Smart Concrete” which can sense its strain and damage

The strain sensitivity of copper powder reinforced concrete

Earthquakes, material deteriorations and other environmental factors challenge the structural safety. In order to protect the lives, structural health monitoring is crucial. The metal foil strain gages have low durability, low sensitivity and can get point wise measurements which are disadvantages. In this study six different concrete mixtures were designed; one without any copper powder, the rest five having different copper powder volume fractions. Three cube samples from each mixture were cast and cured. Simultaneous measurement of electrical resistance and strain were conducted during the compression tests. A strong linear relationship between strain and electrical resistance change was obtained for copper powder reinforced concrete. The results are contribution to the development of “Smart Concrete” which can sense its strain and damage

Temperature and moisture effects on electrical resistance and strain sensitivity of smart concrete

Cement composites, with enhanced electrical properties, have been investigated as multifunctional composites, with application as strain sensors, heating elements or anode in different electrochemical technique. In this work, several aspects regarding the practical application of smart concrete with the addition of brass fibers have been addressed. In general, electrical conductivity of cement composites is dependent on their moisture content and temperature. Therefore, for a real use of this type of sensors the influence of these parameters should be determined. The electrical resistance of the smart concrete decreased linearly with temperature up to 50 °C, therefore this effect can be compensated in strain sensing applications. On the other hand, at higher temperatures, especially after 150 °C, the mismatch strain between brass fibers, cement paste and aggregates resulted in damage, which was detected as an increase of the electrical resistance on the order of 613%. Thus, smart concrete can be used as fire alarm sensor. Also, the relationship between moisture and electrical resistance change was determined. After curing, the samples with moisture content of 5.2% were put in an electric furnace at 90 °C. After 60 min of 90 °C exposure the minimum resistance was measured as 702 Ohm for an average moisture content of 4.8%. At this optimal moisture content, water between fibers was lost and direct contact between fibers was achieved, maximizing the electrical conductivity of the composite. After this point, when the smart concrete was heated for a longer time, the electrical resistance increased almost 300% because water acting as electrolyte was lost. Thus, smart concrete is sensitive to moisture change and can be used as moisture sensor, especially at constructions exposed to harmful water. The effect of moisture content on the strain sensitivity of smart concrete was tested. The mechanism relating piezoresistive properties and moisture content were enlightened. Multifunctional smart concrete can be used as strain, fire and moisture sensor while acting as a load bearing element.This work was supported by The Scientific and Technological Research Council of Turkey (TUBITAK) through Grant no: 213M452 entitled ‘‘Smart Concrete Production”