Effects of multi-walled carbon nanotubes on strength and interfacial transition zone of concrete
- Authors: Van Tonder, P. , Mafokoane, T.T.
- Date: 2014
- Subjects: Carbon nanotubes , Concrete - Mixing , Materials - Testing
- Type: Article
- Identifier: uj:5057 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13619
- Description: Multi-walled carbon nanotubes (MWCNTs) were used to try and eliminate the aggregate interfacial transition zone. Different concrete mixes were used in fixed proportions along with varying concentrations of CNTs. The CNTs were applied in different concentrations, namely, 0.05 wt%, 0.1 wt% and 0.2 wt%, per dry weight. CNTs were dispersed using sonication. Concrete specimens were tested for compressive, flexural and split-tensile strengths. For each test, thirteen mix designs were investigated which included untreated aggregates and CNTs, and treated aggregates and CNTs. The results were compared with the results of the control concrete. The results showed that the use of CNTs improves the compressive, flexural and split-tensile strengths. It was concluded that CNTs minimize the ITZ.
- Full Text:
Effects of sulphuric acid on the compressive strength of blended cement-cassava peel ash concrete
- Authors: Olonade, Kolawole Adisa , Olajumoke, Akinropo Musiliu , Omotosho, Ayoade Oluwaseun , Oyekunle, Funso Ayobami
- Date: 2014
- Subjects: Sulphuric acid , Reinforced concrete , Concrete - Mixing
- Type: Article
- Identifier: uj:5065 , http://hdl.handle.net/10210/13636
- Description: Influence of sulphuric acid on compressive strength of concrete made with blended cement-cassava peel ash was investigated in this study. This is with a view to determining the level of resistance of such concrete to acidic exposure. Cassava peel ash (CPA) prepared from uncontrolled burning was used to substitute cement at 5, 10, 15 and 20% by weight of cement as binder. Concrete mix proportions of 1:2:4 (batching by weight) were prepared with the slump value within 6010 mm while water-binder ratios (w/b) were being noted. A total of 90 cubes of the concrete mixture of sizes 150 mm were cast and cured in fresh water (as control), 0.5, 1.0 and 1.5 M concentrations of sulphuric acid solution (H2SO4) for 7, 28, 56 and 90 days. The compressive strength was determined at the expiration of each curing age. The results showed that the w/b increased with increase in the quantity of CPA in the mixture. Compressive strength of concrete made with cement-CPA as binder and cured in fresh water was comparable to that of normal concrete when up to 15% CPA was used, but relatively low strength was obtained when cured in H2SO4 solutions, depending on the quantity of CPA. Leaching of Porlandite in the concrete cubes was observed with worse condition in the case of concrete containing 20% CPA in sulphuric acid solution of 1.5 M. The compressive strength reduced with increase in concentrations of the acid as well as with increase in the content of the CPA. It is concluded that CPA did not mitigate the adverse effects of sulphuric acid on the compressive strength of blended cement-CPA concrete.
- Full Text:
Radiological assessment of high density shielding concrete for neutron radiography
- Authors: Ekolu, Stephen , Ramushu, Mokgobi A.
- Date: 2014
- Subjects: Concrete , Concrete - Mixing , Concrete blocks
- Type: Article
- Identifier: uj:5070 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13641
- Description: A radiation shield is a physical barrier placed between a source of ionizing radiation and the object to be protected from the radiation. In this research, concrete was selected as the best shielding material. An investigation was carried out to evaluate a specific concrete mixture developed in [1] for shielding of radiation energies. The high density shielding concrete (HDSC) concrete had 28-day compressive cube strength of 30 MPa, w/c (water/cementitious ratio) of 0.51 and density of 4231 kg/m3. It composed of CEM 52.5 N, silica fume, hematite aggregates, steel shots, colemanite and chemical admixtures. This paper presents an evaluation of the shielding properties of the HDSC using foil activation method. It is shown that the HDSC mixture achieved the desired shielding capabilities within the first 250 mm thickness of the concrete block.
- Full Text:
Simple criteria for evaluating sulphate attack in concrete
- Authors: Ekolu, Stephen
- Date: 2014
- Subjects: Concrete - Mixing , Blast furnaces , Slag cement , Concrete
- Type: Article
- Identifier: uj:5082 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13653
- Description: This paper attempts to analyse results from the standard test methods employed for sulphate attack and evaluates their correlations, consistency and contrasts, as well as physical observations. Data from expansions and mass change of 25 x25 x 285 mm mortar prisms and 75 x 75 x 285 mm concrete prisms were used. Mortar mixtures consisted of 1: 2.25: 0.5 cement to sand to water while concrete mixtures were of water-cementitious ratio (w/cm) of 0.45, 0.50, 0.65. Mixtures were made using CEM I 42.5N with or without 30, 50, 70% ground granulated blast furnace slag (GGBS) and stored in sodium sulphate solutions of 28 g/L and 50 g/L as SO4. Results show that ASTM C 1012 mortar expansion criteria of 0.10% corresponds to 1.2% mass gain. Similarly, concrete prism expansion criteria of 0.05% is equivalent to 0.75% mass gain. It is proposed that in the absence of expansion monitoring, the use of mass gain criteria of 1.2% mass in mortar prisms or 0.75% in concrete prisms may be sufficient for evaluating sulphate attack.
- Full Text: