Concrete Engineering

By
O. James ,P.N.Ndoke and S.S.Kolo
Department Of Civil Engineering, Federal University Of Technology.
Minna.

ABSTRACT
Normal concrete was prepared with a water-cement ratio of 0.50. cube specimens were cast for testing the compressive strength at 7 and 28 days of curing respectively using three curing methods namely immersion, sprinkling and Plastic sheeting, curing to cure the cube specimens until the day of testing. Test results indicates that water curing (WAC) as well as sprinkling (spraying) curing provided much better results than membrane (Plastic Sheeting) method of curing. The rate of drying was significant when the specimens were subjected to membrane (Plastic sheeting) method of curing. This thus hampered the hydration process and thus affected the compressive strength property of the hardened concrete. The overall finding of this study suggests that concrete should be cured by water curing to achieve a better compressive strength.

Keywords:
Curing method, compressive strength, concrete
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By Narasingha Mohanta
(Research Officer, Zonal Laboratory (R&B) Balangir)

Abstract:
IS:10262 is the code specified by Bureau of Indian Standards for Concrete Mix Design. The code came to existence in the year 1982. Keeping pace with the advancing technology the code has been revised in December 2009. Significant changes have been made in the revised version and a brief discussion is presented in this paper comparing the two versions of IS:10262. The basic points where the guidelines have been modified are discussed. Besides one numerical example has been solved using guidelines of both the versions to understand the differences. Though the 2009 version encourages mixing of mineral admixtures to meet greater challenges of modern concreting, a simple example is considered with use of no additives.

Introduction
Mix Design of Concrete is the process of deciding the proportions of the ingredients of concrete so as to be produced most economically, that would satisfy the desired properties of fresh and hardened concrete as well. In simpler words, the concrete should be well workable when fresh and the designed compressive strength as well as durability should be achieved at hardening.
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By
Prof. V.D.Gundakalle, Professor ,Department of Civil Engineering, K.L.E. College of Engineering and Technology, Belgaum, Karnataka, (India)

Prof.Abhishek.S.Pathade, Professor, Department of Civil Engineering, K.L.E. College of Engineering and Technology, Belgaum, Karnataka, (India).

Mubashar Munshi Post Graduation Student, K.L.E. College of Engineering and Technology, Belgaum, Karnataka, (India).

Abstract
The actual earthquake force in considerably higher than what the structures are designed for. We cannot design the structures for the actual value earthquake intensity because the cost of construction will be too high. The actual intensity of earthquake is reduced by a factor called response reduction factor ‘R’. The value of ‘R’ depends on how we design the frame members. From previous study it is noted that the ‘R’ factor depends on ductility factor (Rµ), strength factor (Rs), structural redundancy (RR) and damping associated with structure. The objective of this work is to evaluate the response modification factor (R) for RC elevated water tanks supported on framing system are considered having staging height of 15m and 21m with varying capacities and staging configuration. These tanks are designed for gravity as well as seismic loads. A non-linear pushover analysis is used to calculate the base shear capacity and ductility of tanks. Two different cases of collapse criterion are used for defining ultimate stage on the capacity curve. It is observed that the Rµ are increasing with time period but the variation is not consistent. RS is higher for lower staging height.

Key words
Response reduction factor, Seismic design, static nonlinear pushover analysis
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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

Concrete Strength
Cement like water, aggregates and some times admixtures is one of the ingredient of concrete. The mixing of these materials in specified proportions produces concrete. Accordingly cement alone is not a building material, it is the concrete which is a building material. For a given cement and acceptable aggregates, the strength that may be developed by a workable, properly placed mixture of cement, aggregates, and water (under same mixing, curing and testing conditions) is influenced by the :

a) Ratio of cement to mixing water
b) Ratio of cement to aggregates, the strength of the mortar, the bond between the mortar and the coarse aggregate.
c) Grading, surface texture, shape, strength, and stiffness of aggregate particles.
d) Maximum size of aggregate.

Strength of concrete is directly related to the structure of the hydrated cement paste. Air in concrete produces voids. Excess of water in concrete evaporate leave the voids in the concrete. Consequently, as the W/C ratio increases, the porosity of the cement paste in the concrete also increases. As the porosity increases, the compressive strength of the concrete decreases.

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By
Er. Kaushal Kishore ,
Materials Engineer, Roorkee

In about 80% of our construction sites, the water in the concrete mixer is added in a very crude manner either direct from a hoze pipe or by some container without any proper measured quantity. Thus no consideration is given to maintain free Water/Cement ration to its correct specified value resulting production of poor quality of concrete. The addition of mixing water in the concrete mixer with these crude methods always add more water then actually required. This excess water in due course evaporated leaving voids and increasing the porosity of the concrete. Such concrete will have lower strength and also will be not durable.

Therefore it is very important to maintain free W/C ration to its correct value in all the batches of concrete. Free W/C ratio means mixing water added to saturated and surface dry aggregates ie, if the site aggregates are dry extra water is to be added in the mixing water as per the absorption of aggregate, and if the site aggregates contains surface water, this surface water is to be deducted from the mixing water. The weight of aggregates should also be adjusted accordingly. A Concrete Mix Design is reported in standard moisture condition of aggregates and this is saturated and surface dry aggregates. If aggregates are being taken by volume bulking of sand should be taken into consideration.

To solve the construction sites mixing water problems, a simple graduated transparent plastic jar of least count 0.5 ltr, as per drawing should be supplied along with the mixer or may be fabricated at site. This Jar be installed at site near concrete mixer as shown in the drawing. The water may be filled in the jar to the quantity of required gauging water. While mixer is running the measured water in the jar slowly drain in the mixer drum through rubber hoze by opening the valve. If ADMIXTURES are to be used and required to be mixed with the gauging water, this may be mixed with water of the jar.

We at engineeringcivil.com thankful to Sir Kaushal Kishore for publishing his paper on “Water Measuring Jar for Concrete Mixer”.

By
Preetpal Kaur Ragbir Singh, Assoc. Prof. Dr, Nasir Shafiq
University Technology Petronas, Bandar Seri Iskandar.31750,Tronoh, Perak, Malaysia

Abstract
Design, construction and maintenance requirements of tall buildings and industrial complexes are very different from those applicable for normal building design and construction. For example, for conveying the services and other facilities such as water supply, electricity, air-conditioning and sewerage discharge; a complex network of system routing is provided, which usually align vertically and horizontally and spread throughout the floor area. This complex network is often obstructed by the structural components such as beams, columns and floors and requires to penetrate through such obstruction, which is called the structural penetrations. The size, location and configuration of structural penetration are derived from the type of services, magnitude and speed of facility to be provided. The most prevalent location, size and configuration of structural penetration are always an issue between structural engineers and service or facilities design engineers. This research focuses on the effects of static loading on reinforced concrete beams with openings. This research also studies the prospect of strengthening the beams by using external bonded CFRP in different combinations or arrangement to regain bending capacity that was lost due to the openings. The openings are circular, rectangular, square and elliptical shaped.

Keywords
CFRP Sheets, Large Opening, Static, RC Beam.
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By
Prof. Pravin B. Waghmare
Acharya Shrimannarayan Polytechnic Pipri (M)- Wardha-Maharashtra

Abstract
The objective of this study is to identify an efficient retrofitting method for existing open ground story reinforced concrete frame buildings. Failure of several soft-stored buildings in the past earthquakes underscores the need to retrofit existing soft-story buildings. A common cause for the collapse of multi-storied buildings is the occurrence of soft story in the ground floor due to the presence of infill walls in the upper story. During the Bhuj (Gujarat) earthquake of 6thJanuary 2001 several soft storied building failed there by confirming the vulnerability of such buildings to earthquake loading. This underscores the need to retrofit existing soft story buildings to prevent their total collapse. The existing building structures, which were designed and constructed according to early codal provisions, do not satisfy requirements of current seismic code and design practices. A two dimensional R.C. frame designed with linear elastic dynamic analysis using response spectrum method. The computer software package STAAD Pro–2005 is used for dynamics analysis technique is used to assess the performance of a (G + 4) reinforced concrete buildings, of which the ground storey is a parking facility the ground storey is 3.5m high while the upper stories giving a total height of 15.5 m. the building is located in Seismic Zone IV.

The RC frame is retrofitted by three methods namely,
1) Brick masonry infill in the ground story.

2) Steel braces in the ground story.

3) R.C. Structural wall in the ground story.

The study concludes that the building designed as per provisions of IS: 456:2000 using limit state method of design, and analyzed as per existing seismic code IS: 1893-2000 of all these three methods studied the use of structural wall in the ground story panel gave the maximum strength and ductility.

Keywords: Open ground storey, brick infill, RC wall Infill and Steel Bracing.
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By
Guimer Tarek and Mellas Mekki
Department of Civil Engineering, Mohamed Khider University, Biskra, BP 145, Biskra 07000, Algeria
Tel fax: 033 73 45 28

Abstract
This work aims to study the evolution of the resistance of Portland cement pastes and mortars containing two mineral additions such as calcareous filler and finely crushed slag.

The effects of the addition of two mineral additions to Portland cement pastes are mortars, has been carried to evaluate the evolution of the mechanical resistance as function of the age and the mode of the treatment .This study is a simplified approach to show the contribution of the mineral addition on the development of the mechanical resistance, and the porosity obtained using methanol exchange method. In addition, to confirm this study and based on laboratory test resorts approximate equations were obtained

Keywords: Porosities, cement paste, mortar, mechanical resistance, exchange by methanol.
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The reinforcement of concrete pavement is usually in the form of long mesh type. A road usually has length is generally much longer than its width and therefore cracking in the transverse direction has to be catered for in design. Reinforcement is required in the longitudinal direction to limit transverse cracking while transverse steel acts to provide rigidity to support the mesh fabrics. For long mesh in concrete slab, the main weight of reinforcement should be placed in the critical direction (i.e. longitudinal direction) to control cracking. However, if the concrete road is quite wide, certain reinforcement has to be placed in the transverse direction in this
case to control longitudinal cracking.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

The Marshall Mix Design method was originally developed by Bruce Marshall of the Mississippi Highway Department in 1939. The main idea of the Marshall Mix Design method involves the selection of the asphalt binder content with a suitable density which satisfies minimum stability and range of flow values.

The Marshall Mix Design method consists mainly of the following steps:

(i) Determination of physical properties, size and gradation of aggregates.

(ii) Selection of types of asphalt binder.

(iii) Prepare initial samples, each with different asphalt binder content.
For example, three samples are made each at 4.5, 5.0, 5.5, 6.0 and 6.5 percent asphalt by dry weight for a total of 15 samples. There should be at least two samples above and two below the estimated optimum asphalt content.

(iv) Plot the following graphs:

(a) Asphalt binder content vs. density
(b) Asphalt binder content vs. Marshall stability
(c) Asphalt binder content vs. flow
(d) Asphalt binder content vs. air voids
(e) Asphalt binder content vs. voids in mineral aggregates
(f) Asphalt binder content vs voids filled with asphalt

(v) Determine the asphalt binder content which corresponds to the air void content of 4 percent

(vi) Determine properties at this optimum asphalt binder content by reference with the graphs. Compare each of these values against design requirements and if all comply with design requirements, then the selected optimum asphalt binder content is acceptable. Otherwise, the mixture should be redesigned.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.