Assessment of a fire damaged reinforced concrete building

Arup Ghatak,P.N. Ojha,Singh Brijesh,Singh Abhishek,Reddy TVG,Mohapatra B N 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.1

A proper condition assessment of reinforced concrete structure after a fire event involves field and laboratory work to determine the extent of fire in order to design an appropriate and cost effective repair scheme. The present paper presents a case study where an attempt has been made to carry out a condition assessment of a fire damaged building in a systematic manner. The approach adopted broadly consisted of questioning of on-site personnel, a detailed visual survey, on-site non-destructive / partially-destructive tests, collection of in-situ samples from site along with some laboratory based investigations on samples collected from site. Differential Thermal Analysis (DTA), X-Ray Diffraction (XRD) Analysis and Scanning Electron Microscopy (SEM) Imaging were conducted for microstructural characterization and analysis of concrete to correlate, corroborate and validate the results obtained through on-site assessment. Since the building was an old structure, carbonation depth in structural members was also evaluated. Finally, based on the visual inspections indicating the condition of surface and structural elements such as spalling, exposure and condition of reinforcement, cracks, honeycombing etc. along with NonDestructive Test / Laboratory test results, the repair methodology of structural members are presented.

Appraisal of geopolymer lightweight aggregates sintered by microwave radiations

Nimra Saleem,Khuram Rashid,Noor Fatima,Sadia Hanif,Ghinwa Naeem,Aamna Aslam,Miral Fatima,Kiran Aslam 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.2

This work was designed for the production of geopolymer based lightweight aggregate (LWA) using industrial by-products. Combination of fly ash (FA) and silica fume (SF) were used as precursors, whereas, combination of sodium hydroxide and sodium silicate were used as activator. Small amount of sodium bicarbonate was also used for surface hardening and early strength development. Pellets of dif-ferent sizes were crafted manually and cured by microwave radiations just for 5 minutes. The physico-mechanical properties of produced pellets (LWA) were discussed in light of: morphology, density, water absorption, specific gravity, porosity, aggregate impact value, and particle crushing strength. The prop-erties of LWA were also compared with literature reported synthetic LWAs cured with different tech-niques. The water absorption and specific gravity of LWAs were within the specified range provided by ACI standard. Mechanical strength properties briefed that the produced LWAs were strong enough to resist compressive load comparable to natural LWAs and many other synthetic LWAs. Thus, proposed curing method, microwave irradiation, has been found to be a sustainable and fast curing technique than conventional energy-intensive curing regimes. The results also confirmed that produced LWAs have po-tential to replace natural LWAs both in cast-in-place and precast concrete elements with possible eco-nomic, environmental, and technical benefits.

Influences of nylon fiber geometries and contents on me-chanical behavior of reinforced mortar

Teeranai Srimahachota,Haruka Matsuura,Shun Yamaguchi,Hiroshi Yokota 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.2

Used nylon fishing nets were utilized as recycled nylon (RN) short fibers for reinforcing ce-ment mortar. Fishing nets were cut into specified shapes and lengths, then mixed into mortar. In this study, the influences of fiber geometries such as diameter, aspect ratio and the fiber content on the me-chanical properties of mortar were emphasized. Changes in flowability of fresh mortar, compressive strength, flexural strength, failure behavior, flexural toughness, residual strength factors were experimen-tally investigated and compared among various mixes. Experimental results indicated that fiber geome-tries as well as fiber content directly affect the mechanical properties of mortar. Adding fibers was found to reduce flowability and compressive strength of the mortar. For instance, using sharp-shapes reduced compressive strength by 41% while using cross-shapes improved flexural strength by 44.5%. Improve-ment in flexural strength and flexural toughness were found in association with the fiber content. RN fiber contributes to the post-peak loading capacity and prevents abrupt failure of concrete structures.

Evaluation of mechanical and durability properties of con-crete made with Indian bottom ash as replacement of fine ag-gregate

P. N. Ojha,Amit Trivedi,Brijesh Singh,Abhishek Singh 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.2

Bottom ash is a major by-product of the coal-based power generation process and it has particle size ranging from 45 μm to 150 μm. As per current provisions of IS: 383-2016, bottom ash can be used as replacement of natural fine aggregate up to 25% in case of lean concrete (less than M15 Grade) only. However, its use in reinforced and plain concrete is not permitted. Therefore, it is imperative to study the feasibility of using coal based bottom ash as a replacement of conventional fine aggregates (i.e., natural and crushed sand) in plain and reinforced concrete to increase the utilization of this industrial byproduct. In this study, natural and crushed sand were replaced with bottom ash at various percent-ages for prepa-ration of concrete and study its effect on fresh, hardened and durability properties of concrete. Bottom ash was collected from Vindhyachal thermal power plant of India. Experimental studies were conducted at w/c ratio of 0.65 and 0.40. Concrete mixes were studied and analyzed for various mechanical and durability properties. Based on fresh concrete properties i.e., workability, slump retention and strength development, it was observed that up to 50% replacement of conventional fine aggregate with bottom ash is technically feasible.

Optimization and evaluation of ultra high-performance concrete

P. N. Ojha,P. N. Ojha,Abhishek Singh,Brijesh Singh,V. V. Arora 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.1

Ultra-High Performance Concrete (UHPC) has been defined as a cementitious based compo-site material with compressive strength above 150 MPa and enhanced durability via its discontinuous pore structure. The microstructure of UHPC is denser and more homogeneous in comparison to conventional concrete. UHPC has several advantages over conventional concrete but the use of it is limited due to the high cost and limited design codes. Methodology for production and development of UHPC needs to be established. The paper covers both optimization and evaluation of Ultra-High-Performance Concrete along with highlighting the importance of packing density, mixing procedure and curing regimes containing a high volume of mineral admixture and ultrafine materials. Cementitious content of all the mixes in the study was kept in the range of 1000 kg/m3 and water to binder ratio was kept as 0.17. This study focuses on the methodology to be adopted for optimizing the packing density of UHPC, the challenges associated with it and their influence on compressive strength.

Evaluation of Polymer Modified Mortar and Bonding Agent for Structural Repair

Ojha P N,Kaura Puneet,Singh Brijesh,Daniel Y N,Kumar Nitesh 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.2

Polymer modified mortar is found to be suitable for structural repair and strengthening of damage structural elements. Conventional mortar is not preferred in repair of concrete since it has inferior mechanical property and durability performance. Polymer based mortar is an alternative to conventional mortar with enhanced mechanical properties. However, there are limited specifications and guidelines available for specifying PMM mixes for structural repair work. The research work aims to evaluate the mechanical performance of polymer based mortar with varying concentration of styrene butadiene rubber latex at laboratory scale. Another aspect in repair of corrosion damage structures is the bond between the substrate concrete and repair mortar. In order to study the effectiveness of bonding agents, the performance evaluation of bonding agents has been evaluated using slant shear test and pull-off test as per ASTM C 882 and EN 1542 respectively. Findings of study indicates that at 8-10 percent concentration of dry polymer solid by cement mass in polymer based mortar is the optimum dosage. Styrene-butadiene rubber based polymer mortar showed improvement in flow in comparison to normal mortar however, mixes with crushed sand shows decrease in flow which is due to presence of more fines. Slant shear and pull-off test method shows epoxy bonding agent give better bond strength as compared to SBR latex.

The durability and rehabilitation technologies of concrete sewerage pipes: A state-of-the-art review

Zhuge Yan,Fan Wei,Duan Weiwei,Liu Yue 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.2

This paper reviews the literature available on the subject of the durability of concrete sewer pipes and the corresponding rehabilitation technologies. An introduction related to the importance of the sewer system in urban life and its durability issues was first discussed as most people did not recognise the scale and complexity of the underground sewer system. Then the recent development of alternative binder materials or filler materials to improve the acid resistance of concrete was specified. For instance, the effects of alternative binders on the hydration products and the mechanism of biogenic corrosion were discussed in detail. The paper ends with the current rehabilitation technologies and the structural performance of rehabilitated sewer pipes. Also, some suggestions associated with future research were made.

Bond and durability investigation of basalt fiber and PEN fiber reinforced composites for concrete applications

최동욱,김영호,Batzaya Baasankuu,CHINZORIGT GOMBOSUREN 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.1

Bond and durability characteristics of basalt fiber reinforced polymer (BFRP) and polyethylene naphthalate (PEN) fiber/PEN FRP were investigated. Magnitude and distribution of the bond stress between BFRP/PEN FRP and concrete were investigated by double lap shear test. Four different types of durability test were performed: (1) Beam bond test following accelerated conditioning protocols by ACI 440.9R using plain concrete beams strengthened with BFRP or PEN FRP; (2) tensile test of PEN fiber/PEN FRP after immersion in 1N NaOH, 3% NaCl solutions, and water up to 6 months; (3) tensile test of PEN fiber/PEN FRP after immersion in 5% and 10% diluted solutions of HCl; and (4) exposure to natural outdoor environment. Bond test results indicated high bond stress developing over relatively short distance for BFRP that has high elastic modulus (EBF = 68.4 GPa) while relatively low bond stress developing over longer length for PEN FRP that has low elastic modulus (EPEN = 17.4 GPa). In the beam bond test, very good behavior was shown by PEN FRP after 4 month’s exposure to wet and alkaline conditions while moderate behavior was shown by BFRP. Overall, the performance of PEN fiber/FRP was satisfactory in all durability tests conducted in this study.

Effect of clay as deleterious material on properties of normal-strength concrete

Harish R. Choudhary,Saha Dauji,Arham Siddiqui 아시아콘크리트학회 2020 Journal of Asian Concrete Federation Vol.6 No.1

Sustainability concerns prompted use of crushed aggregates in concrete, wherein deleterious materials might get inadvertently included. Some deleterious materials are allowed up to limiting values by most standards, which, however, are silent about the quantification of their effects on properties of concrete – which would be site specific. For an important Indian infrastructure, this study quantifies effects of clay fines as deleterious material in concrete, on workability (slump) and strength (cube compression; split tensile; flexural tensile tests) around the limit (1% of fine aggregates by weight) stipulated by the Indian standard. The novelty of the study is that, contrary to the literature in this domain, the effects are studied without alteration of the mix proportions – a different practical scenario. The limit of clay fines in concrete allowed by Indian standard was found to be adequate considering strength parameters, but for maintaining target workability, the limit would be revised to 0.5% of the fine aggregates. Generally, the variations of concrete properties with the increasing clay fines were: (1) the workability and split tensile strength reduced monotonically, in non-linear fashion; (2) compressive strength (beyond 7 days) and the flexural tensile strength (modulus of rupture) reduced monotonically in linear manner.

Development of methodology for design of grade slab using numerical approach

M.K. Sharma,s. Dauji,P.K. Srivastava,K. Bhargavaa 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.1

Presently, the design of grade slab for heavy industrial floors is generally carried out by empirical approaches, as provided in different national or international literature. With advances in numerical methods and computational resources, efforts have been made to apply numerical approaches in analysis of grade slab or pavements; however, such applications have been primarily restricted to the research area. For practical industrial implementation, numerical analysis methodology for design of grade slab is scarce in literature. In this article, a methodology for analysis of grade slab for practical design is developed with parametric analysis using commercial finite element software SAP2000® . The results are compared with empirical approaches for validation. The method proposed would be useful for practicing engineers for the design of grade slabs using numerical analysis.