Sharma Shashi Kant
Civil Engineering Department, National Institute of Technology Jalandhar, Punjab, 144011, India.
Heliyon. 2019 Aug 12;5(8):e02081. doi: 10.1016/j.heliyon.2019.e02081. eCollection 2019 Aug.
Self compacting concretes (SCC) containing higher volumes of pozzolanic materials possess compressive strengths up to 30MPa. Fibers like steel, polypropylene, and carbon fibers are added in small volumes ranging from 0.25-2% v/v of concrete to increase the strength (>40MPa) of such concretes as higher volumes of fiber cause balling effect on account of inhomogeneity, thereby reducing the strength and workability. Hence higher volume of cement substitution either with mineral admixtures or fibers, or with both, to increase strength and workability is limited in the case of SCC. The condition worsens further if recycled aggregates replace normal aggregates. Wollastonite micro fiber (WMF) is a promising material that could be used in higher contents but its interaction with recycled aggregates to affect workability and strength has not been studied. Therefore this study tries to obtain a high strength concrete (>M40) by use of WMF along with flyash @ 5%, maximally up to 10% each. Microsilica was added @ 2.5%, maximally up to 10% to improve the interphase strength and make the concrete homogeneous. Results indicated that in order to obtain a high strength mix for such composites, higher amounts of WMF (≥10% by weight of binder) such that WMF:flyash varies from 1:1 to 2:1 is required, along with microsilica contents ≥7.5%. Literature suggests 5% microsilica along with either 20% WMF or 10% flyash, for yielding high strength SCC without recycled aggregates. Hence use of nearly equal amounts of WMF, flyash, and microsilica such that nearly 30% of cement is substituted, is recommended.
含有较高火山灰质材料用量的自密实混凝土（SCC）的抗压强度可达30MPa。钢纤维、聚丙烯纤维和碳纤维等纤维以0.25 - 2%（体积比）的小用量添加到混凝土中，以提高此类混凝土的强度（>40MPa），因为较高用量的纤维会因不均匀性导致结团效应，从而降低强度和工作性。因此，在SCC中，用矿物掺合料或纤维，或两者同时使用来大量替代水泥以提高强度和工作性是有限的。如果用再生骨料替代普通骨料，情况会进一步恶化。硅灰石微纤维（WMF）是一种有前景的材料，可以大量使用，但尚未研究其与再生骨料相互作用对工作性和强度的影响。因此，本研究试图通过使用WMF以及5%（最高可达10%）的粉煤灰来获得高强度混凝土（>M40）。添加2.5%（最高可达10%）的微硅粉以提高界面强度并使混凝土均匀。结果表明，为了获得此类复合材料的高强度混合料，需要较高用量的WMF（≥胶凝材料重量的10%），使得WMF:粉煤灰的比例在1:1至2:1之间，同时微硅粉含量≥7.5%。文献表明，对于不使用再生骨料的高强度SCC，使用5%的微硅粉以及20%的WMF或10%的粉煤灰。因此，建议使用近乎等量的WMF、粉煤灰和微硅粉，使得水泥替代量接近30%。
