An evolutionary approach to modelling concrete degradation due to sulphuric acid attack

Concrete corrosion due to sulphuric acid attack is known to be one of the main contributory factors for degradation of concrete sewer pipes. This paper proposes to use a novel data mining technique, namely, evolutionary polynomial regression (EPR), to predict degradation of concrete subject to sulphuric acid attack. A comprehensive dataset from literature is collected to train and develop an EPR model for this purpose. The results show that the EPR model can successfully predict mass loss of concrete specimens exposed to sulphuric acid. Parametric studies show that the proposed model is capable of representing the degree to which individual contributing parameters can affect the degradation of concrete. The developed EPR model is compared with a model based on artificial neural network (ANN) and the advantageous of the EPR approach over ANN is highlighted. In addition, based on the developed EPR model and using an optimisation technique, the optimum concrete mixture to provide maximum resistance against sulphuric acid attack has been identified

Effect of potassium-chromate and sodium-nitrite on concrete steel-rebar degradation in sulphate and saline media

In this paper, effect of potassium-chromate (K2CrO4) and sodium-nitrite (NaNO2) on concrete steel-rebar degradation in sulphuric-acid and in sodium-chloride media were studied. Electrochemical monitoring of open circuit potential and compressive strength effect of the different concentrations of these admixtures in steel-reinforced concretes immersed in the acidic/marine-simulating environments were analysed for detailing admixture performance. Results subjected to ASTM C876 interpretations showed that concrete admixed with 0.145 M potassium-chromate exhibited optimum inhibition effectiveness with good compressive strength improvement in the acidic medium. In the saline medium, the concrete admixed with 0.679 M sodium-nitrite exhibited optimal inhibition performance, but with reduction in concrete compressive strength

Marks rating system – an approach in condition assessment and prioritization of sewer rehabilitation – a case study

Abstract Marks rating system is a simple system that can be used to evaluate the condition of sewer pipes and to determine the prioritization for rehabilitation purposes of sewer pipes and sewer infrastructures. The system provides a consistent approach for assessing the impact of pipe failure, coding defects and assigning priorities for rehabilitation of sewer pipes. Each sewer segment is separately evaluated based on several considerations such as inspection results, impact rating factors, frequency of defects, and engineering and administrative factors. The marks of defects were assigned in such a way that the worst condition has the highest mark. The factors considered by applying marks system were identified from questionnaires that were prepared and distributed by the author to technicians, engineers, heads of departments and managers of municipalities of several cities in Iraq. The case study includes seventeen concrete sewer pipes in the municipality of Al Diwaniyah city – Iraq. CCTV inspection was carried out to determine the marks of the structural and performance defects. Results of marking rating system applied on the seventeen sewer pipes showed that MP#12 has the worst condition with highest marks of 38. Sewer pipes MP#1 and MP#7 have the best condition with lowest marks of 18. The prioritization of rehabilitation should have descending ordered from the highest to lowest mark.</jats:p

Mechanical Properties of Concrete Incorporating Pre-Treated Wastes Sawdust

This paper investigates the effect of using wastes sawdust as a replacement of fine aggregate (sand) on mechanical properties naming compressive, tensile and flexural strengths of ordinary Portland concrete. The wastes sawdust was treated before incorporating it in concrete mixtures. Three different methods were used to pre-treat the sawdust including a) soaking the sawdust in distilled water at 50 oC, b) soaking the sawdust in Ca (OH)2 solution, and c) soaking the sawdust in Ca (OH)2 solution and using a set accelerator in the concrete mixture. In addition to the control mixture (having no sawdust), three more concrete mixtures were prepared to explore the effect of the three different methods of pre-treatment on the mechanical properties of concrete. Results showed that the compressive strength of the concrete incorporating wastes sawdust pre-treated with the calcium hydroxide solution (slaked lime) and having the accelerator was higher than that of the control mixture. The tensile and flexural strengths of the concrete mixture having waste sawdust pre-treated by Ca (OH)2 solution and having the accelerator were found to be very comparable to those of the control mixture. On the other hand, the compressive, tensile, and flexural strengths of the concrete mixture with sawdust pre-treated by Ca (OH)2 solution only were somehow comparable to those of concrete mixture having sawdust pre-treated by distilled water. While the compressive strength of the concrete mixtures incorporating sawdust pre-treated with either Ca (OH)2 solution or distilled water was less than that of the control mixture, both tensile and flexural strengths of the two treated concrete mixtures were approximately comparable to those of the control mixture.</jats:p

Reinforced lime columns: a new technique for heave control

Excessive volume changes of expansive soil cause severe damage to civil structures, which costs billions of dollars in annual repairs. In this paper, the optimum ratio of lime to soil weight to maximise the efficiency of lime columns as a technique to reduce the swelling of expansive soil is investigated. A new technique to further enhance the efficiency of the lime columns technique in reducing soil swelling is also investigated, namely reinforced lime columns. The new technique involves reinforcing the lime columns using reinforcement bars attached to the foundation of the structure. The experimental study involved laboratory-scale tests of expansive soil beds treated with lime columns supporting model foundations. The experimental results showed that the optimum lime content is 6% (by weight) of the soil within the column. It was found that the lime columns technique minimised the swelling of the expansive soil by 33%. In the meantime, the reinforced lime columns reduced the swelling of an identical soil bed by 69%. The results also showed that the swelling of the expansive soil decreased with an increase in the ratio Lcol/Dsoil (the ratio of the length of lime columns to the depth of expansive soil). Des changements de volume excessifs dans les sols expansifs endommagent gravement les structures civiles, ce qui entraŷne des réparations annuelles se chiffrant à des milliards de dollars. Dans cet exposé, nous étudions la proportion pondérale optimum de chaux dans la terre en tant que technique servant à réduire le gonflement d´un sol expansif. Nous é tudions é galement une nouvelle technique destinée à améliorer encore davantage l´efficacité de la technique à colonnes de chaux pour réduire le gonflement du sol, nommément des colonnes de chaux renforceès. Cette nouvelle technique consiste à renforcer les colonnes de chaux en utilisant des barres de renfort attachées aux fondations de la structure. L´étude expérimentale passe par des essais en laboratoire sur des lits de sol expansif traité avec des colonnes de chaux supportant des fondations modélisées. Les résultats montrent que la teneur optimum en chaux est de 6% (en poids) de sol à l´intérieur de la colonne. Nous avons trouvé que la technique des colonnes de chaux réduit de 33% le gonflement du sol expansif. Par ailleurs, les colonnes de chaux renforcées réduisent de 69% le gonflement d´une couche de sol identique. Les résultats ont montré é galement que le gonflement d´un sol expansif diminue en proportion avec l´augmentation du taux Lcol/Dsol (longueur des colonnes de chaux par rapport à la profondeur du sol expansif). </jats:p

Resistance of Recycled Aggregate Concrete (RAC) Subjected to Drying-Wetting Cycles to Attack of Magnesium and Sodium Sulfates

Recycled aggregates were widely used in the concrete industry as a replacement of natural aggregates in the last two decades. In this study, the resistance of concrete mixtures having various levels of recycled aggregate as a replacement of natural coarse aggregate to the attack of magnesium and sodium sulfates was investigated. Five mixtures made with 0%, 25%, 50%, 75%, and 100% recycled aggregate were partially immersed in magnesium and sodium sulfate solutions having concentrations of 2.5%, 4.5%, and 6.5% and subjected to drying-wetting cycles for a total of 10 weeks. Mass losses of concrete specimens owing to the attack of sulfate solutions and the effect of drying-wetting cycles were recorded weekly. Results show that the incorporation of recycled aggregate decreased the compressive strength of concrete at ages of 7 and 28 days. The decline in the compressive strength was more significant when the replacement percentage exceeds 50%. Mass losses of concrete specimens were found to be increased as the level of recycled aggregate increased. Mass losses of concrete specimens having 100% recycled aggregate were approximately as twice as those of concrete specimens having 0% recycled aggregate owing to 10 weeks of partial immersion in magnesium sulfate solutions of concentrations of 2.5%, 4.5%, and 6.5%. The attack of sodium sulfates was less aggressive than that of the magnesium sulfates. Results also show that the reduction in the compressive strength is directly proportional to the mass loss following a linear equation of R-squared value of 0.937.</jats:p

Resistance of Recycled Aggregate Concrete (RAC) Subjected to Drying-Wetting Cycles to Attack of Magnesium and Sodium Sulfates

Recycled aggregates were widely used in the concrete industry as a replacement of natural aggregates in the last two decades. In this study, the resistance of concrete mixtures having various levels of recycled aggregate as a replacement of natural coarse aggregate to the attack of magnesium and sodium sulfates was investigated. Five mixtures made with 0%, 25%, 50%, 75%, and 100% recycled aggregate were partially immersed in magnesium and sodium sulfate solutions having concentrations of 2.5%, 4.5%, and 6.5% and subjected to drying-wetting cycles for a total of 10 weeks. Mass losses of concrete specimens owing to the attack of sulfate solutions and the effect of drying-wetting cycles were recorded weekly. Results show that the incorporation of recycled aggregate decreased the compressive strength of concrete at ages of 7 and 28 days. The decline in the compressive strength was more significant when the replacement percentage exceeds 50%. Mass losses of concrete specimens were found to be increased as the level of recycled aggregate increased. Mass losses of concrete specimens having 100% recycled aggregate were approximately as twice as those of concrete specimens having 0% recycled aggregate owing to 10 weeks of partial immersion in magnesium sulfate solutions of concentrations of 2.5%, 4.5%, and 6.5%. The attack of sodium sulfates was less aggressive than that of the magnesium sulfates. Results also show that the reduction in the compressive strength is directly proportional to the mass loss following a linear equation of R-squared value of 0.937