Civil Engineering Science

This work is a continuation of the development of a model for predicting the potential of Portland cements to exhibit expansion due to delayed ettringite formation (DEF). The model was derived based on kinetics theory applied to cement chemistry and evaluates two primary conditions -the presence of sufficient active alumina in cement and the requirements for sulfate-to-alumina ratio applied against the countering microstructural effects -to determine the underlying kinetic characteristics for DEF in the system. The primary purpose of the model is determination of the intrinsic presence of the potential for DEF in cements. In this second part of the work, the model is validated and tested for robustness by its application to a wide range of existing experimental data for DEF studies, taken from various global sources available in the literature. Over 169 data sets taken from various independent works were used in the validation and the model was found to be in strong agreement with experimental data for both expansive and non-expansive cements. However, a few outputs showed disagreement between model predictions and experimental observations. Most of the important disparities appear to occur with cements of high Fe 2 O 3 /Al 2 O 3 ratios and may be related to the inadequacy of the Bogue formula used in the model. These aspects reveal where future refinement of the model is required. The model at this stage is applicable to plain Portland cements with a future possibility of improvements to examine more complex systems containing pozzolanic materials.

This paper presents an investigation on a deteriorated slab of a two-story building located in Johannesburg, South Africa. The structure has been in use as a residential building for more than 60 years. The top slab of the first floor was delaminated and reinforcement bars were severely corroded. Condition assessment of the building was done using the Schmidt hammer test, cover-meter survey and half-cell potential measurements. In addition to the non-destructive tests done, X-ray diffraction and scanning electron microscopy were also conducted on the deteriorated concrete.

Pervious concrete was investigated for potential use as a permeable reactive barrier (PRB) for treatment of acid mine drainage (AMD). Pervious concrete mixtures of various water/cement ratios (0·50, 0·40, 0·35, 0·30, 0·27) and cement contents (300, 360, 380, 400 kg/m3) were prepared. Dolomite and granite aggregate types, size 9·5 mm, were employed. The tests performed were density, compressive strength and porosity. Water treatment was determined by analysis of the influent and effluent AMD after passage through the pervious concrete. It was found that a filter thickness of at least 500 mm was required to increase the pH of acidic mine water from 2·8 to between 5 and 7, and achieve a corresponding reduction in electrical conductivity. When used in the filter mix design, the granite aggregate gave better treatment performance in comparison with the dolomite aggregate. The concrete PRB treatment led to the effective removal of major metals from the AMD. The treatment reduced the metal...

STEPHEN EKOLU is a lecturer in construction materials engineering at the University of the Witwatersrand. For six years, after obtaining his BSc, he worked in diff erent capacities as construction site engineer in materials testing and in research. He then obtained an MSc (Eng) with distinction from the

A consortium of three durability index test methods consisting of oxygen permeability, sorptivity and chloride conductivity were used to evaluate the potential influence of four (4) common SANS 10197 cements on strength and durability of concrete. Twenty four (24) concrete mixtures of water-cement ratios (w/c's) = 0.4, 0.5, 0.65 were cast using the cement types CEM I 42.5N, CEM II/A-M (V-L) 42.5N, CEM IV/B 32.5R and CEM II/A-V 52.5N. The concretes investigated fall in the range of normal strength, medium strength and high strength concretes. It was found that the marked differences in oxygen permeability and sorptivity results observed at normal and medium strengths tended to vanish at high concrete strengths. Also, the durability effects attributed to use of different cement types appear to diminish at high strengths. Cements of low strength and/or that contained no extenders (CEM 32.5R, CEM I 42.5N) showed greater sensitivity to sorptivity, relative to other cement types. Resu...

This paper describes an examination of concrete cores drilled from an old motorway bridge that had manifested deterioration and was in need of repair. Site observations and the nature of cracking indicated that alkali-silica reaction was suspect. Cores taken from the damaged structure were analyzed by using optical petrography for potential presence of reactive phases in aggregates, and chemical analyses to estimate the residual alkali content in the concrete. Results from the test methods were consistent with existence of alkalisilica reaction damage mechanism in the concrete. The level of severity of alkali-silica reactivity appeared to be moderate. The diagnostic features determined from tests indicate with some certainty, that alkali-silica reaction might have partly or solely contributed to distress in the bridge structure.

Mortars are used extensively in accelerated methods of testing the physical properties of cementitious materials. Mortar strength is invariably used to determine cement strength grade of cements and for general evaluation of material behavior, as typically employed in research and testing. Presently, the South African (SA) cement industry imports standard from Europe for cement testing purposes. This study was conducted to formulate South African standard sand that could be used to conduct mortar strength tests for compliance to specifications and for general research purposes. Two formulations of local South African silica sands, referenced as SA513S and SA413S, were developed to suit standard gradings. The formulated South African standard sands (SASS) where tested in comparison with European standard sand (ENSS) of EN196-1 and American graded standard sand (GSS) of ASTM C-778. Following the formulation and grading of SASS, mortar mixtures of 1:3:0.5 cement to sand to water were cast in 50 mm cubes and tested for compressive strength for ages up to 90 days. Two types of cements were employed in the tests, the ordinary Portland cement CEM 1 42.5N and pozzolanic cement CEM V 32.5N. Comparison of the 28-day compressive strength results between the four SS types showed an excellent agreement, giving standard deviations of 1.96 and 2.51 for CEM I and CEM V. The flow results for the standard sand types varied, with EN196-1 giving the highest mortar flow followed by GSS sand and SA413S. The GSS and SA513S gave precisely the same flow results. The investigation indicates the SASS may be suitable for use with SA standard specifications for mortar strength tests.

Small and medium construction enterprises (SMEs) are an important vehicle to drive the economic growth globally. However, this enterprise sector has been constrained by different factors that stifle their full participation in the main stream economy specially credit accessibility. There is paucity of research to verify the determinants that predict revolving credit accessibility from financial institutions in South Africa. The data was obtained using questionnaire survey. 179 small and medium contractors responded from conveniently sampled respondents in Gauteng province in South Africa. The data was analysed using Statistical Package for the Social Sciences (SPSS) version 22. The study found that the dependant variable i.e. revolving credit was not predicted by the independent variables suggested i.e. gender, age group, current position, organization ownership, tax number, location and collateral. The finding informs bank managers they should not force clients to submit collateral before awarding credit to the SMEs. The suggested model that was tested attained the Hosmer and Lemeshow Test goodness of fit hence the results were credible. However, a further study is proposed for the entire country as the researchers acknowledge limitation on the chosen location of study.

This paper presents long-term results and microscopic analyses for a six-year experimental study on the effectiveness of lithium nitrate in mitigating delayed ettringite formation (DEF) with or without alkali-silica reaction (ASR). In the previous publication [1], interesting findings were found showing that lithium nitrate is effective in controlling DEF or ASR-DEF mechanisms in concretes. In the present study, microstructural features associated with microcracking and ettringite infilling showed relatively reduced intensity of internal distress and damage when lithium nitrate was admixed in DEF expansive concrete. Microanalysis done using plots of Al/Ca and S/Ca shows that, the use of lithium nitrate leads to formation of non-expansive ettringite similar to normal early-age ettringite formed in moist-cured concretes. These observations give some insights into the mechanism responsible for mitigation of DEF by lithium nitrate.

In the literature, the effects of curing, sheltering and CO2 concentration under natural carbonation are not fully understood. There is either controversy or limited research available regarding these factors, while most investigations are based on accelerated carbonation. The currently available research on natural carbonation is particularly constrained and limited. From a practical viewpoint, natural carbonation is more important as it represents the behavior of real structures. This paper reviews the influences of different curing methods and their durations; sheltered and unsheltered exposure conditions, and different atmospheric CO2 concentration levels, on carbonation of concrete under the natural outdoor exposure environment. The various curing methods examined are moist-curing, steam-, air-and oven-curing. It is found that curing effects are coupled with the type of cement. For cements containing no more than 30% fly ash or 50% slag, three-day curing is sufficient to stabilize long-term strength and carbonation behavior of concrete under site conditions. Different types of normal curing do not significantly alter natural carbonation behavior. An equation is suggested which accounts for the effect of unsheltered outdoor exposure on carbonation. Also, correction factors are proposed to account for different atmospheric CO2 levels under natural carbonation.

The aim of this study was to develop a gravity feed column setup and to set the flow parameters based on experimentally measured flow rates and pressure drops. Prior to the present study the authors used a column setup in which acid mine drainage was pumped through pervious concrete filled columns, using electrical peristaltic fish pond pumps. The gravity feed setup in the present study was designed to overcome the need to rely on electrical power supply. The study describes the design setup of four gravity columns. The design requirements comprised determination of appropriate column sizes, pressure heads and hydraulic gradients required to produce a low flow rate of about 1 mL/min at outlets of the columns filled with pervious concrete media. Of special interest is the hydraulic gradient being responsible for continuous flow in each column. Following completion of the design setup , continuous flow rates of 0.60 to 0.80 mL/min were attained with a Reynolds number of about 4.0 in the columns filled with pervious concrete. Further research is in progress involving employment of the gravity-feed system for acid mine drainage treatment investigations.

It has recently been shown that pervious concrete is a promising, effective technology as permeable reactive barrier for treatment of acid mine drainage (AMD). However, pore clogging also occurs simultaneously during AMD treatment. In the present study, mixtures of pervious concrete were made and used in a column experiment during which pore clogging occurred in the samples. Pore volume, connectivity and other parameters of pervious concrete were evaluated using five (5) different methods comprising the volumetric method (VM), linear – traverse method (LTM), image analysis (IA), falling head permeability test and X - ray micro - computed tomography. It was found that pervious concrete effectively removed from AMD, about 90 to 99% of various heavy metals including Al, Fe, Zn, Mn and Mg. Cr concentration significantly increased in the treated effluent, owing to leaching from cementitious materials used in mixtures. The VM and LTM gave statistically similar pore volume results, while I...

Use of durability index (DI) is one of the several approaches that have been used or advanced through various test methods for the purpose of evaluating the durability of concrete mixtures. In South Africa, use of DI’s has developed through testing and research over the past years. A consortium of three tests of oxygen permeability index (OPI), water sorptivity and chloride conductivity are employed. This paper presents an investigation conducted to determine the effect that superplasticizers may have on durability indexes of concrete. Concrete mixtures of strengths ranging from 30 to 50 MPa were cast using two types of commercially available superplasticizers, herein referred to as GL and RSP. The admixtures were of different chemical bases with RSP being a sulphonated naphthalene superplasticizer while GL was a polycarboxylate ether superplasticizer. The tests conducted were compressive strength, oxygen permeability and water sorptivity. It was found that use of GL increased the c...

Durability characteristics of cement mortars and concrete are of interest to various researchers and practitioners in the field of construction materials engineering. This study evaluated the potential use of a semi-synthetic zeolite additive for improvement of cement mortar properties. The product, a blend of selected alkaloids and zeolite is commercially available and effectively used in soil stabilization for road construction. However, its influence and effectiveness on properties of cementitious systems has not been explored. Emphasis of this study was on durability of cement mortars. This was assessed using the durability index approach being advanced in South Africa. The additive was added to standard mortars of 0.5 water-cement ratio, prepared according to EN 196, in proportions of 0%, 0.4%, 0.6%, 0.8%, 1.0%, and 2.5%. Tests carried out include compressive strength, oxygen permeability, sorptivity and resistance to sulphate attack. It was found that the additive significantl...

A model is proposed based on the statistical concept of the overlapping distribution method (ODM). The model is thenapplied to estimatethe number of students thatcan beexpected to qualify for and to passsupplementaryexaminations.TheODM prediction model was validated using 19 sets of examination events involving 858 civil engineering students in twodifferent universities. It was found that lowering the mark cut-off criteria from 45 to 40%, increases the number of studentsthat qualify for supplementary examinations, by up to 75%. In turn, the number of students that successfully sit forsupplementary examinations, increases by about 40%. The proposed model promises to be useful in informing policy onconflicting issues that arise from balancing the work load under large class sizes on one hand, and offering wideropportunity to as many students as have the potential to pass

In this paper, data are used to show that countries with high record of publications and patents are either developed or those countries that are strongly developing. Mastery of existing scientific knowledge and intensification of engineering and scientific research emerge as the two important ingredients that are necessary for industrial development. Current trends in research show inklings of research growth in SubSaharan Africa. However, the limited growth in research at an advanced level is presently a critical barrier and a major challenge.

Problems of lack of rural development, low-cost housing and the urban poor are recognised features of endemic complex limitations of modern construction technologies, government policies and market forces to achieve balances of sustainable societal development. There is however a continuous struggle through science and technologies to improve the human conditions of living. Along these efforts, the cross-cutting issues arising from industrial exploitation of cement and concrete are espoused delving into their sources, with suggestions for a multidisciplinary, multifaceted network approach as an effective channel for innovative progress. Advanced technologies, while valuable, are not in themselves the ultimate solution to rural development but selective intermediate technologies could significantly be effective for development. It is argued that, the concept of sustainable development in Sub-Saharan Africa (SSA), and other developing economies, require a unique definition and focusse...

Hintergrund Viele gastroenterologische Krankheitsbilder gehören zu den sehr häufigen Erkrankungen im niedergelassenen Bereich (Prävalenz der Dyspepsie 25-40 %, des Reizdarmsyndroms 7-25 %, der Divertikulose 50 %, der Gallensteine 20 %, der peptischen Magenerkrankungen 15 % und der gastrointestinalen Tumorerkrankungen 25 %). Im Gegensatz zu anderen Schwerpunktfächern fallen im Bereich Gastroenterologie nur 20 % der Patienten unter die zehn häufigsten Schwerpunktdiagnosen im stationären Bereich (chronische Leberkrankheiten, Diabetes mellitus, Dickdarmkrebs, Bauchspeicheldrüsenerkrankungen, Gallensteine, Gastritis, Speiseröhrenerkrankungen, Enteritis). Die anderen 80 % verteilen sich über eine Vielzahl von Diagnosen, sodass das Fach eine sehr große Zahl unterschiedlicher Erkrankungen des Verdauungstrakts, der Leber und des Pankreas umfasst. Diese Erkrankungen werden schwerpunktmäßig von 1.200 niedergelassenen Ärzten mit der Gebietsbezeichnung Gastroenterologie und 1.650 im Krankenhaus tätigen Gastroenterologen betreut. Derzeit gibt es 500 gastroenterologisch orientierte Fachabteilungen an deutschen Krankenhäusern. Nach Angabe der Landesärztekammern bestehen 536 Einrichtungen mit einer Weiterbildungsermächtigung (40 im Bereich der Universitätskliniken), wobei 60 % davon über eine volle Weiterbildungsbefugnis verfügen.