في الصحراء الليبية الواقعة في منطقة الجنوب الغربي يتم نقل المياه الجوفية من مواقع الآبار إلى مناطق إستغلالها لغرض الشرب وللأغراض الزراعية والصناعية. خطوط الأنابيب المعدنية هي الأكثر إستعمالاً لنقل تلك المياه. أغلب هذه الأنابيب تعرضت مع الزمن لحالات متفاوتة من التآكل الداخلي مما سبب خسائر إقتصادية وفاقد بكميات المياه المنقولة. بعض هذه الأنابيب تدهورت حالتها وتم إستبدالها بأنابيب أخرى بنفس النوعبة. ولما كان السبب الرئيسي لحصول التآكل الداخلي في الأنابيب وتدهور حالتها هو نوعية المياه الجوفية التي تجري فيها، وبما أن الأنابيب الجديدة ستقوم بنقل نفس النوعية من المياه فإن تلك الأنابيب مع الزمن ستتعرض أيضاً للتآكل وتتكرر الخسائر الإقتصادية والفقد بكميات المياه التي ستتسرب خارج الأنبوب. ولغرض التمكن من معالجة المشكلة وتجنب إستمرار حصول مثل هذه الخسائر الإقتصادية والفاقد بكميات المياه المنقولة ، لذا يجب التحري ومعرفة الأسباب الأساسية لذلك تم في هذه الدراسة التحري موقعياً عن العوامل الأساسية للمياه الجوفية الموجودة في منطقة الجنوب الغربي من ليبيا التي تسبب حصول مثل هذا التآكل في الأنابيب المعدنية. وفى هذه الدراسة تم تجميع عينات للمياه الجوفية من مجموعة منتخبة من آبار الضخ المنتشرة في أجزاء منطقة الدراسة وهي سبها ومرزق وغات ووادي الشاطئ ونقلها للمختبرات في طرابلس وإجراء التحليلات الكيميائية لها ومعرفة نوعية وتركيز المكونات الكيميائية لكل عينة. حيث أظهرت نتائج التحاليل وجود نسبة عالية من الغازات الذائبة فى المياه الجوفية وهى الأكسجين الذائب وثانى أكسيد الكربون الذائب وهى السبب الرئيسى فى زيادة نسبة التآكل فى الأنابيب المعدنية، إقترحت الحلول المناسبة لحماية مثل هذه الأنابيب من التآكل الداخلي والسيطرة عليه وبذلك سيتم التمكن من تلافي حصول الخسائر المائية والاقتصادية في منطقة الدراسة. Abstract In the south western of Libya, groundwater is transported by metallic pipes from wells to the consumers for drinking, domestic, agricultural and industrial purposes. Some of the used pipes have been corroded internally; consequently quality of the transported water was contaminated, this situation caused health and economical effects to residences, also losses in water by leakage through pipes. The goal of this study is to study the factors that might cause such problem. The area of study is located in south western part of Libya (Murzuq basin). Chemical properties of samples from 45 wells were collected and analyzed.Results showed higher concentrations of O2 and CO2, normal values pH, and traces of H2S. The internal corrosion of the metallic water pipelines in the district was related to the effects of high levels of O2 and CO2. The study recommended treating the excess of the CO2 and O2 before its use and using pipes types that resist the corrosion from the water.
رجاء محمد صقرعلى (2010)

Two-stage concretes, despite the fact that they have proven themselves in various types of construction, have not been studied to the same extent as traditional heavy concretes. Therefore, the article developed the composition of frame concrete with various additives in the composition of the cement-sand mortar. A comparison of the mechanical characteristics of the developed compositions with the addition of silica fume (SF) and superplasticizer (SP) in various combinations. In addition, test specimens were prepared with combinations of water/cement ratios of 0.45, 0.55, and 0.85, and cement/sand ratios of 0.5, 1, and 1.5. A total of 36 mixtures were prepared, silica fume was introduced as a partial replacement of cement in the amount of 6 wt.%. And a superplasticizer equal to 1.2 % of the cement content was added to the water. Compressive strength tests on two-stage concrete cylinders were carried out in accordance with ASTM-C873 and ASTM-C943. Tensile strength was also tested on 3 samples of each composition in accordance with the procedure described in ASTM-C496/C496M. As a result, the development of the strength of two-stage concrete for 7, 28 and 120 days was studied. It was found that the overall compressive strength of the two-stage concrete based on SF, SP and SF + SP was higher than in concrete without any additives. At the same time, the modified concrete has higher strength properties, because it provides better contact due to expansion, as well as by reducing the water-cement ratio in grout. The results obtained allow to design a cement-sand mortar capable of filling all the voids between the coarse aggregate, thereby creating a dense structure of two-stage concrete. arabic 9 English 58
Hakim S. Abdelgader(5-2019)

Two-stage concrete (TSC) is known by various names such as colcrete, Polcrete, preplaced aggregate concrete and prepacked concrete. It is different from traditional concrete in two fundamental ways, namely method of construction and mix proportion. Two-stage concrete (TSC) is defined as firstly, coarse aggregates are placed into the formwork and grout is applied to fill in the between coarse aggregate particles voids. Secondly, the percentage of coarse aggregates in the mix proportion of TSC is higher than that in normal concrete. The typical value is about 60% as compared with 40% in traditional concrete. As coarse aggregates are preplaced first, they can occupy up to 60–70% of the total volume. As coarse aggregates are not involved in the mixing process, TSC is environmentally friendly with lesser consumption of energy. With a higher content of aggregates, TSC reduces the use of cement by 20–30% and may minimize the temperature rise. Engineering properties of TSC, including its stress–strain relationship, is mainly governed by the properties of coarse aggregates as stress is transferred from the skeleton of aggregates to hardened grout. Main advantages of TSC include a higher volume of coarse aggregates and the ability to use larger size coarse aggregates. The latter also reduces the cost of crushing. TSC has beneficial properties such as low drying shrinkage, high bonding strength, high modulus of elasticity, and excellent durability. The method of TSC has proved particularly useful in a number of applications like underwater construction, and masonry repair, where placement by conventional methods is extremely difficult. The method is also applicable in case of massive concrete where low heat of hydration is required. It is studied the feasibility of casting two stage concrete with 100% steel slag as coarse aggregate. In term of formulation, to adopt two stage concreting method we could minimize the risk of concrete bleeding and segregation due to high water absorption and quite high density of slag aggregate. The effect of slag coal ash and foamed glass on the mechanical properties of two-stage concrete has rarely been reported. Thus, the development of an eco-efficient alkali-activated grout for two-stage concrete is a new research topic that has no robust results to draw solid conclusions and it should blaze the track towards a cleaner production of building materials with outstanding sustainability.
Hakim S. Abdelgader(1-2022)