Indian Concrete Journal

Concrete as an artificial rock: Mineralogy of aggregates revisited Swathy Manohar, Mohammed Haneefa Kolakkadan, Bahurudeen A., B. S. Dhanya, Manu Santhanam

Concrete is a conglomerate of aggregates encapsulated in a continuous matrix of binder phase. Concrete is comprised of aggregates more than 70 % by its volume and has a significant influence on the quality of concrete. Irrespective of the binder used, aggregates impart volume stability, stiffness and inertness to concrete. These properties are governed by the geochemistry of aggregates, which depends on the mineralogy. Currently, various sources of aggregates are used in the concrete production. A combined study on aggregate mineralogy, its influence on aggregate properties and performance in concrete is imperative to enable proper selection and effective utilization of available aggregate resources. This paper reviews the mineralogy of aggregates with respect to their geochemistry, and discusses the relevance pertaining to engineering properties, physical, chemical, and thermal constancies. Moreover, the paper also provides a colour atlas of common minerals in aggregates.

Study on the influence of volcanic ash modification on alkaline Portland cement Nanfu Qiao, Yizhen Wang, Qihua Liu, Mengyuan Zhao

This paper used volcanic ash as the chief modifier to improve Portland cement. The effect of raw material proportioning on compressive strength, slump, and mass loss of cement was investigated. The results revealed that with the decrease of the amount of volcanic ash, the slump of the sample reduces gradually. The amount of volcanic ash is 445~544 kg/m³, and the slump is in a moderate position, which can have a good strength (48.84~64.55 MP_a) under suitable construction difficulty. When the mass ratio of volcanic ash, cement, sodium hydroxide, and sodium silicate is 433:76:60:6, the strength of the specimens reached up to 69.86 MP_a. The mass loss of different groups to reach stability was almost the same, and the mass loss of all groups reached the relative stability level in about 30 days. Nevertheless, the addition of volcanic ash increased the mass loss of cement specimens. While the ratio of volcanic ash, cement, sodium hydroxide, and sodium silicate is 445:78:49:4, the slump is 153 mm and can have sufficient strength (62.19 MP_a) under decent construction challenge, it is recommended for practical application.

Influence of mortar composition on flexural and impact performance of ferrocement panels for usage in secondary roofing V. Roopa, M. J. Abdul Latheef, M. S. Haji Sheik Mohammed

In tropical countries, maximum heat gain in buildings is through roof slab, which necessitates the provision of insulation to improve the comfort of inhabitants. Secondary roofing using ferrocement panels is one the effective methods of heat insulation. This study analyses the flexural and impact performance of ferrocement panels made with three types of cement mortars (control mortar, silica powder-modified mortar, and metakaolin-modified mortar), mesh types (crimped wire mesh, and galvanized welded wire mesh) and different mesh layers (single and double). Ferrocement panels of sizes 900 × 300 × 25 mm (18 nos.) and 600 × 600 × 25 mm (12 nos.) were cast to study the flexural behavior and the impact strength respectively, as per relevant standards/methods. The test results indicate that the ferrocement panels with two mesh layers and metakaolin-modified mortar exhibited significantly increased flexural strength, as compared to other tested categories. All the flexural test specimens were observed with the formation of flexural cracks in the tension zone, followed by crushing of mortar beyond ultimate load, in the middle one-third region. Impact test results revealed a significantly improved energy absorption for two mesh layer specimens as compared to single mesh layer specimens. It can be concluded that the ferrocement panels cast with two mesh layers, and metakaolin-modified mortar offered improved flexural, and impact strength and is recommended for use in secondary roofing.

Assessment of mechanical properties of concrete with hybrid fiber reinforcement in low volume fraction R. Shanthi Vengadeshwari, H. N. Jagannatha Reddy, R. Prabhakara

Concrete is made of chemically active material - cement and volume rigid inclusions - aggregates. Behavior of concrete is expressed by the properties both at fresh and hardened stage. Structural elements are formed using concrete which are subjected to external loads. Since behavior and strength of structural elements are affected by mechanical properties, modification in them is very important for effective performance of structure. Fibers when used in both mono fiber reinforced concrete (MFRC) and hybrid fiber reinforced concrete (HFRC) considerably improve mechanical properties compared to plain concrete. It was reported that MFRC with low modulus fibers result in improved strain capacity, reduced crack width and lesser compressive strength. In the present study, it is intended to evaluate and compare the impact of steel and basalt fibers in mono form and hybrid form in the mechanical properties of high strength concrete. To evaluate the mechanical properties of M40 grade fiber reinforced concrete, volume fractions chosen were 0.25, 0.5, and 0.75 %. Addition of basalt fibers with steel fibers improves synergetic response to a considerable extent. From the overall assessment of the mechanical properties, it was established that the combination of basalt, and steel fibers at 0.25, and 0.75 % respectively produced optimum results.