13 Records out of 22207 Records

Laterized quarry dust and recycled concrete as alternative building materials

Author: Musembe, Timothy Musiomi

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2009

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Building materials ; Concrete ;

Abstract:

The use of conventional materials is facing two main challenges of high cost and large-scale depletion of the sources thus creating environmental problems. These challenges demand that alternative materials be explored that are not only affordable but are also environmentally friendly. In this regard, laterized quarry dust and recycled concrete are proposed as possible alternative building material. To date, extensive studies have been done on laterite, quarry dust and recycled aggregates, separately. However, there is lack of data on performance of blended materials as well as large scale tests on structural elements made from the alternative materials. This research therefore seeks to assess the performance of blended alternative materials when used in concrete and blocks. In the study, samples of materials were investigated to determine basic properties following which the optimum proportions of ingredient materials were determined for concrete and block mix. Finally, the viability of using the materials was assessed for large scale concrete beams and wall panels. The results demonstrate that there is great potential of laterized quarry dust concrete and blocks. When recycled concrete aggregates are used, 300/c, of river sand can be replaced with laterized quarry dust and still attain compressive strength of 20 N/mm2? In addition, the flexural capacities of alternative as well as conventional concrete beams were found to be within 5%. The fmdings are intended to contribute to sustainable construction of low cost housing and development.

Investigation into the residual strength of reworked reinforcement bars in reinforced concrete structures

Author: Mwero, John Nyairo

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 2007

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Concrete ; Steel ; Materials science ;

Abstract:

Reinforced concrete is a major material of construction in this country. A key component of this material is steel reinforcing bars. Sometimes these bars are bent wrongly, straightened and re-bent, resulting in the altering of their original characteristics. Some of such steel has been known to be used whereas some has been condemned as unfit for reinforcing purposes. This dissertation reports on investigation into the residual properties of reworked steel including yield strength, ultimate strength, modulus of elasticity and ductility. Comparison of these has been done against those of normal reinforcement bars using stress strain plots resulting from tensile tests. A comparison of the behavior of reworked steel as opposed to that of normal steel bars in reinforced concrete has also been done using bending tests on reinforced concrete testbeams built some using normal and others reworked bottom reinforcement bars. In these tests, load-deflection relationship, beam side strains and ultimate load were investigated. From the investigations residual crookedness and cracking during the rework were found to cause reduction of yield and ultimate strength of the reworked bars by up to 3 %. Reworkingwas also found to reduce ductility. The reduction was however small and the reworked bars were found to still meet the codes' requirement for minimum elongation. More than half the number of reworked bars tested broke away from the reworked region, an observation suspected to be the result of work hardening on the region of the rework. Further work could be done with a large enough number of samples to satisfy statistical requirements, and to vary the number and amount of rework to establish a relationship between property change and number / amount of rework. This can then be used to suggest modifications on the current design formulae and to look into the practicality of having a design based on serviceability and checked at the ultimate limit state, since it has been established that the reworked bars might be good within the serviceability limit.

Use of local labour crushed aggregates as a low cost aggregate for low cost housing.

Author: Mutunga, Charles Mekeku

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2004

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Building materials ; Affordable housing ; Concrete ; Housing ; Labour ;

Abstract:

Shelter is one of the basic human needs. It is important that good and safe housing units are constructed by all. Concrete is one of the most widely used Engineering materials. It is therefore important to produce good quality concrete using locally available materials especially aggregates to meet the housing needs of the poor. This thesis project undertook to study local labour produced aggregates, their production, physical and mechanical properties. After describing the aggregates, the study further embarked on determination of the properties of ordinary and reinforced concrete that this labour produced aggregates made. Further, the properties of these aggregates and the concrete they made were compared with those of machined aggregates and the concrete they produced. The challenge, therefore, was to produce concrete of good quality at the highest possible level of economy. Labour produced aggregates through the tests performed produced concrete of very good quality. Labour crushed aggregates produced concrete with a compressive strength of 23 N/mm2 compared to machine crushed aggregates concrete compressive strength of 19 N/mm2 at 28 days for a compressive design strength of 20 N/min2? The reinforced concrete beams made of labour crushed aggregates had a higher flexural strength, 7.48 Nzmnr' than those made of machine crushed aggregates, 4.87 N/mm2 at 28 days for class 20 concrete. As coarse aggregates occupy the largest volume of concrete, a cheap and easily available aggregate, labour produced aggregate, will make it possible for both rural and urban poor people to be able to afford better, strong, safe, durable and serviceable housing units. Further research has been recommended for future consideration in areas not covered in this study and can lead to further reduction in cost of concrete and subsequently in construction using concrete. Keywords: Labour produced aggregates, properties of aggregates and concrete.

Flexural behaviour of large scale concrete elements reinforced with bamboo

Author: Maritim, Nelson Kipkemboi

Awarding University: Jomo Kenyatta University of Agriculture and Technology, Kenya

Level : MSc

Year: 2004

Holding Libraries: Jomo Kenyatta University of Agriculture and Technology Library ;

Subject Terms: Civil engineering ; Concrete ; Bamboo ;

Abstract:

This research study is on bamboo culms as an alternative material for concrete reinforcement in low cost housing. In this research the commonly found bamboo species in Kenya Arundiraria Alpina was used to reinforce concrete beams, which were then subjected to flexural test. Other tests like tensile, compression, shear, pull-out test of bamboo and steel in concrete were also done in order to understand the basic properties of bamboo as a reinforcement material. Various tests such as compression, tension splitting and flexural testing prisms were also conducted on the concrete, in order to ensure that the concrete used met the required standard. The strength tests of bamboo obtained and those of previous investigations carried out by other researchers depict bamboo to be a fairly strong material that can be used as a substitute for steel reinforcement. The mean tensile strength of seasoned bamboo is 197.61 Nzmm' and 251.28 Nzmm? for bamboo with and without nodes respectively. The average composite strength of bamboo reinforced concrete beams is 105.5 Nzmm- at 28 days, which is about a half the actual tensile strength of seasoned bamboo. The average Elastic modulus of bamboo is 23.31kN/mm2 for seasoned bamboo and the mean interfacial bond strength of quarter bamboo in concrete is 1.99 Nzmm? at 28 days, which is about 25 % that of structural steel in concrete, which was determined as 7.78 Nzmm- at 28 days. The results show that splitting of bamboo reinforcement into different shapes ???improves the interfacial bond because the newly exposed surface is rougher than the outer surface. Also, it is noted that arranging bamboo reinforcement splits with their concave facing upwards (HBU and QB) enhances bamboo reinforcement stiffness than those with their concave facing downwards (HBD) and whole bamboo culm (FB). This resulted to higher composite strength in HBU and QB reinforced concrete beams than those ofFB and HBD reinforced concrete beams. It is concluded that the use of splitted longitudinal aligned continuous bamboo in the reinforcement of concrete gives rise to significant improvement of the mechanical properties of concrete. The recommendation is made that bamboo pieces with an average width of 20mm and with their concave part facing upwards, could be used to reinforce concrete beams.

Stress strain relations for steel fibre reinforced concrete beams in shear

Author: Nyomboi, Timothy

Awarding University: Moi University, Kenya

Level : MPhil

Year: 2001

Holding Libraries: Moi University Margaret Thatcher Library ;

Subject Terms: Concrete ; Civil engineering ;

Abstract:

Fibre reinforced concrete is a relatively new construction material, with increasing application by the construction industry worldwide. Steel fibres have been found to offer significant increase in the shear strength of plain concrete. Recent research has shown that steel fibre reinforced concrete beams exhibit ultimate shear strengths of the same order as those obtained from conventionally reinforced beams (with stirrups) even at a fibre volume of 0.25%. This can be quite advantageous when used in structural members such as ring, lintel, and foundation beams because problems associated with fabrication and placement of conventional steel stirrups, labour and overall costs can be reduced. However, the limiting factor in the use of this material for the purpose discussed above is the lack of design guidelines that can be used in the design for shear in the structural members utilising the material. As a contribution to the development of design guidelines, evolution of the shear stress - strain behaviour in steel fibre reinforced concrete beams was investigated and linear limit and ultimate strengths were determined. Seventeen beams with varying shear span to depth ratio and steel fibre content were tested in three point bending while monitoring the load and the strains at selected points. The beams were reinforced in bending using steel bars with steel fibres as the shear reinforcements. Twelve cylinders with same fibre content as that of the beams were tested in compression while monitoring the load and strains (horizontal and vertical). Theoretical predictions of the non-linear behaviour based on a modification of hooke's model in which a strain dependent factor is introduced and a more advanced model based on the Imam et.al [23] were made and the two models could describe the experimental results satisfactorily. The prediction of the non-linear behaviour of the shear stress strain - strain was quite good from the two models particularly for the 0.5% steel fibre content. It was established that the linear limit is about 67% of the ultimate shear strength on average. The design application of the two proposed models with steel fibres as shear reinforcements and the classical design method of using shear links was made based on a practical design situation of ring/lintel beam. With the worst condition of loading on the design beam chosen, it was established that the shear stress that arise in lintel / ring are not so high to warrant the use of shear links and could be replaced by steel fibres with use of the proposed models for design.

Strength characteristics of bamboo : structural application in bamboo-reinforced concrete.

Author: Mwaura, Stephen Mburu

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1996

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Bamboo ; Concrete ; Building materials ;

Abstract:

ABSTRACT NOT AVAILABLE

Constraints to the dissemination and utilization of fibre, concrete roofing tile and stabilized soil block technologies in Kenya.

Author: Omayi, Moraa Matilda

Awarding University: University of Nairobi, Kenya

Level : MA

Year: 1993

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Fibers ; Concrete ; Soils ; Building materials ;

Abstract:

ABSTRACT NOT AVAILABLE

Mechanical properties of sisal fibre reinforced concrete.

Author: Mutua, Joackim Mukumbu

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1993

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ; University of Nairobi Upper Kabete Library ;

Subject Terms: Civil engineering ; Concrete ; Hemp ;

Abstract:

ABSTRACT NOT AVAILABLE

Properties of local pozzolanic materials for use in concrete.

Author: Wahome, Ephantus Rubiro

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1990

Holding Libraries: University of Nairobi Jomo Kenyatta Memorial Library ;

Subject Terms: Concrete/Building materials/ ;

Abstract:

ABSTRACT NOT AVAILABLE

The effects of ions on mortar cubes made with Kenyan cements and sands.

Author: Thiong'o, Joseph Karanja

Awarding University: University of Nairobi, Kenya

Level : MSc

Year: 1987

Holding Libraries: National Council for Science and Technology Library ; University of Nairobi Chiromo Library ;

Subject Terms: Chemistry/Building materials/Cement/Concrete/ ;

Abstract:

A study of the effects of aggressive solutions on mortar cubes made from Kenyan ceme.nts and sands , has been conducted. The study is important because failure of concrete structures exposed to rain water, domestic and industrial effluents is increasing. Ordinary portland cement; sulphate resisting portland cement; and pozzolanic cement were used to make 70.7 mm cubes with British Standard sand and suitable sand samples from Kajiado and Machakos districts. The cubes were immersed in: deionised water; waste water from a factory; two concentration solutions of fluoride, chloride and sulphate prepared from the respective acids. The effect of the solutions on the cubes for a period of six months was monitored by measuring volume changes and compressive strengths of the cubes; pH, anionic and cationic concentrations of the solutions. The results for the cubes made with the standard sand were used to assess the performance of the cements. The performance of the sands was assessed by holding the different cements constant in the tests. Kajiado sand has been found to be more coarse and to contain more silt than the Machakos one. Machakos sand, on the other hand, has been found to be richer in mineral content~. Quartz has been found to form the bulk of the two sands. Machakos sand has been found to form unworkable mixes with cements when using a W/C ratio of 0.4, and to bulk when using a W/C of 0.5. The waste water from the factory has been found to contain the following levels of anions: sulphates 361.8-2566.5 ppm; chloride 298.2-1498.8 ppm; fluoride 5.5-38.9 ppm; and phosphate 0.306-1.224 ppm. The solutions have been found to affect the cubes differently. In environments rich in sulphate ions but combined with other ions, like industrial effluents, sulphate resisting portland cement should be u~ed o~ly after a careful study. The reactions of the cubes with the fluoride solutions have been found to be less deleterious than with the other ions investigated and in some cases fluoride ions were beneficial. The cement-sand combinations that were found to have perfo~med well in the different environments are: EnvironmentCement Sand Deionised water Ordinary Portland Machakos Industrial waste water (investigated) Pozzolanic Kajiado or Machakos Fluoride Ordinary Portland Kajiado or Machakos Chloride Pozzolanic Kajiado Sulphate Sulphate resisting Kajiado These cement-sand combinations are recommended to be used in similar environments.