Heat curing practice in concrete precasting technology – problems and future directions

Abstract: While heat curing is mostly used in the precast concrete industry, freshly cast insitu concretes can also potentially attain high temperatures even without artificial heat application. The demands of the modern construction industry coupled with advances in cement manufacture promote the use of high early strength cements and high cement contents. These factors in addition to hot weather conditions in tropical countries, and large concrete pours may raise concrete temperatures to levels similar to those of heat cured concretes. This article attempts to give an overview of the modern application of heat curing practice, discusses problems associated with exposing concretes to undesireably high temperatures at an early age. Current needs and recent developments associated with delayed ettringite formation are highlighted while potential future advancements are speculated

Cronbach’s alpha reliability coefficient in engineering assessments – a preliminary study on possibilities and precautions

Abstract: This paper attempts to apply the Cronbach’s alpha to engineering studies. There is hardly any available literature or research on application of this method to engineering course assessments. Alpha coefficient is commonly used in psychometric tests, as a measure of estimating internal consistency. The data used in this preliminary study consisted of five modules taught over five years by different instructors..

Contribution to diagnosis of alkali-silica reaction in a bridge structure

Abstract: 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 alkali-silica 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

A review on effects of curing, sheltering, and CO2 concentration upon natural carbonation of concrete

Abstract: 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..

Simple hydration equation as a method for estimating water-cement ratio in old concrete

Abstract: Hydration studies done several years ago by R.H. Mills, built on the work of T.C. Powers and other researchers to derive a relationship between the ultimate degree of hydration and water-cement ratio (w/c). This paper reviews the αult-w/c hydration equation for possible application to w/c estimation in hardened concrete. Unlike current methods, the empirical method based on hydration equation has the merit of simplicity but its accuracy has not been tested and proved. A χ2-test statistic showed a good agreement between values of original w/c and estimated w/c for pastes hydrated for 448 days. Accuracy seemed particularly good for mixtures of portland cement only. The method is sensitive to the C3A content while use of extenders in mixtures appears to reduce accuracy. These and other shortcomings are discussed including the effects of advances in cementitious material systems. The need for modifications and development towards an improved method is highlighted

Proposed method of evaluating the eligibility criteria for supplementary assessments

Abstract: During assessments, the results of an examination or test are assigned into a category of pass or fail. In engineering studies and most other disciplines, the pass/fail category is determined from grading of assessments, typically requiring allocation of a quantitative mark achieved by a candidate, in a given module or course program. Institutions have well-defined policies on mark criteria used to determine the pass/fail category. However, quite a challenging issue arises from the category of students whose performance falls within the pass/fail borderline, typically 40 to 51% mark category..

Correlation between formative and summative assessment results in engineering studies

Abstract: This paper attempts to study the relationship between results of formative and summative assessments. Generally, there is limited research work available in this subject, most especially relating to engineering education. The study is conducted using data of modules lectured to undergraduate civil engineering students over a period of 10 years. It consists of data sets for 409 students under nine (9) assessment events of various modules..

Model validation and characteristics of the service life of Johannesburg concrete structures

ABSTRACT: Fifteen (15) reinforced concrete structures consisting of buildings in greater Johannesburg city area and major bridges at various motorway intersections were surveyed for active carbonation deterioration. This has been part of an ongoing field study conducted on the structures since 20001. The data collected were used to validate a degradation model which was subsequently applied for probabilistic analysis of service life of the structures. The statistical variability for durability design parameters of compressive strength, carbonation depth, and carbonation rate were established. The field data verify the validity of an environmentally sensitive carbonation deterioration model. The probabilistic assessment results are compared with findings of the deterministic approach1