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.

Empirical equation and experimental validation of shear parameters for high strength concrete (HSC)

Brijesh Singh,Ojha P N,Patel Vikas,Trivedi Amit,Singh Abhishek 아시아콘크리트학회 2021 Journal of Asian Concrete Federation Vol.7 No.2

With many benefits of the high strength concrete (HSC) the more brittle behaviour that leads to sudden failure makes it important for proper understanding of its behaviour and safe and efficient estimation of capacities. Research on the behaviour of HSC has been extensively carried out since last decade. HSC has higher tensile strength hence a higher cracking shear can be expected. This paper analyzes the different international standards available for estimating concrete’s component of shear strength for reinforced cement concrete (RCC) beam. Different important factors mainly strength in compression, steel reinforcement (dowel action), ratio of shear span and depth, size effect i.e. depth along with the aggregate type (density of concrete) contributing to shear stress (Tc) of concrete has been also analyzed and thereafter, an equation has been proposed to compute or predict Tc value for concrete of both normal and higher grade or strength. The proposed equation has been validated by experimental results wherein 12 RCC beams (with and without reinforcement for shear) were cast and tested to fail in shear. The experimental results validated the proposed equation with considerable factor of safety keeping in view the sudden and brittle nature of failure in concrete in case of shear.

Service Levels of Sidewalks for Pedestrians under Mixed Traffic Environment Using Genetic Programming Clustering

Rima Sahani,Abhishek Ojha,P. K. Bhuyan 대한토목학회 2017 KSCE JOURNAL OF CIVIL ENGINEERING Vol.21 No.7

This study aims at developing a model for pedestrian to evaluate service measure at the roadside walking environment from the qualitative and quantitative analysis in developing countries. The potential primary factors influencing service measure of pedestrian were summarized taking consideration to heterogeneous traffic flow condition and perception of road users. Total 735 real-time sense of participant's satisfaction when they are using the sidewalks, road geometric as well as operational characteristics of the road segments were collected from the 73 sites. The selected sites belong to midsized cities with varying geometric features. Different statistical investigations like factor analysis, Wilks’ lambda test and stepwise regression analysis were carried out to develop PLOS model for sidewalk facilities. From the results it has been observed that the variables taken such as width of sidewalk, vehicle volume, pedestrian volume etc. are significantly influencing the pedestrian service measure and the model was validated with a significance value of R2 = 0.972. The PLOS scores got from the model are then classified using Genetic Programming clustering to find the six PLOS ranges (A-F) which show score for PLOS A ≤1.8 with best condition and PLOS F > 5.1 having worst condition of service.

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.

Comparison of creep models and experimental verification of creep coefficients for normal and high strength concrete

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

A concrete structure when subjected to sustained load presents progressive strain over time, which is associated with the creep phenomenon. The creep characteristic of high strength concrete as-sumes importance in the back drop of increase in prestressed concrete constructions. The paper covers the comparison of creep coefficients with different creep models like Bazant’s B-3, ACI, AASHTO, GL-2000 and FIB model code 2010 for concrete mixes having water to cementitious ratio of 0.47, 0.36, 0.27 and 0.20. The comparison of different models are done for a relative humidity of 60 percent and design life of 100 years. For comparison of creep coefficient using different models the age at loading are kept as 7, 28 and 365 days. Thereafter, values are compared with experimentally obtained results of concrete mixes having water to cementitious ratio of 0.47 and 0.20 for age at loading of 28 days and up to 180 days loading period. Time induced creep strain of high strength concrete is determined using creep rig of capacity 2000 kN. Creep strains are measured at regular time intervals on concrete designed with water to cementitious ratio of 0.47 and 0.20 wherein fly ash and silica fume were also used.

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.