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Eingeladener Vortrag
- nein (10)
Starches and its derivatives are known to exhibit viscosity modifying characteristics. In an ongoing work, the influence of com and cassava starches on some properties of concrete such as compressive strength, heat of hydration and creep are examined. Various percentages (0.0, 0.5, 1.0, 1.5 and 2 %) of starches by weight of cement were added to concrete mixes prepared in the laboratory. Preliminary results of compressive strengths showed that both starches have some positive impact (e.g. there was 5.3 % increase in strength due to a 1 % addition of com starch by weight of cement in comparison to the control while cassava starch of the same percentage gave 4.9 % increase in strength) at certain percentages of starch addition to concrete at 28 days. The creep and hydration results shows the starch additions compares well and in some instance performs better.
As soon as cement is mixed with water, the hydration reaction starts to set of. The progression of the hydration process is governed by the amount and the availability of water and its possibility to access the unhydrated cement grain surfaces. For a total hydration cement theoretically requires water amounting approximately 0.38 of its own mass. Nevertheless, due to the cement’s highly hygroscopic nature, already the moisture in the ambient air can cause first hydration reactions to set in upon the cement grain surfaces. Such pre-hydration processes have an effect on the cement's properties. Dpending on the specific conditions during the storage the significance of the impact on certain properties can vary.
If cement is consumed soon after production and is transported only short distances in a silo wagon to its final destination for immediate use without further stock transfer, the effects are rather negligible. However, if cement is delivered in bags, transported over long distances, shifted serval times and stored for longer time periods until it is finally consumend, these effects can be quite severe. Due to the actual logistical situation with comparably few cement plants, large delivery distances and partially less developed infrastructures, the latter scenario pictures the situation for the most cases in Africa quite well.
In order to verify the relevance of the pre-hydation for practical application, a series of tests was conducted at the German Federal Institute for Materials Research and Testing (BAM). The influence of the cement storage on gresh and hardened concrete properties was investigated for different concrete and mortar types. The investigations show that the impact of the storage conditions is more pronounced for specialized concretes with high sophisticated optimized mixture compositions containing admixtures. Nevertheless, the effects also occur for ordinary concrete and should not be ignored.
Rheological Optimisation for Flowable Mixture Compositions Specified for African Boundary Conditions
(2013)
This report is based on a three-year experience as coordinator of the ACP-EU funded SPIN project. The project involved eight African and three European partners. Practical and unforeseeable problems are addressed that occurred during the project implementation and ways how they were successfully solved are reported. The major problems in many African institutions were administrations that are not used to work in multi-national consortia and a lack of institutional support for the African researchers. In Europe a misjudgement of the African boundary conditions as well as inflexible administrations caused problems. Finally the funding scheme did not always allow to easily overcome the high number of unexpected practical problems. A major deficit identified during the project was a general trend in Africa to underestimate the role of research for the development of the continent. Most universities focus on teaching applied sciences, which is without doubt important to cover the market need for qualified staff in the rapidly growing African industries. However, this makes it unattractive for highly qualified performers to conduct research on the continent. Furthermore this leads to the situation that the curricula can only contain second hand knowledge. In order to attract international high level researchers, it is suggested to install multi-national regional excellence research centres that only promote PhD and post-doc research on a level that can cope with highest international excellence. High level research is often perceived as not capable of focusing on immediate actual problems that many African economies have to cope with.. However, it is considered to be very sustainable in terms of autonomy and mastering future challenges.
Rheological optimisation for flowable mixture compositions specified for African boundary conditions
(2013)
To date concrete technology is not yet well established in sub-Saharan Africa but considering the construction technological challenges of the region, without doubt, concrete will play a major role in future. The social, economic, and geographic boundary conditions distinguish greatly from those that can be found in many other regions of the world, where concrete is considerably well established. Düring the last decades, concrete technology underwent a rapid evolution process, but in most countries, where concrete is already well established, innovations are difficult to be brought into practice, Africa, currently has the opportunity and potential, of directly establishing the best available practice in concrete technology.
The conclusion is drawn that self-compacting concrete (SCC) or highly flowable concrete is a reasonable solution for African construction sites. Since on most African construction sites the disadvantageous concreting environment is the most crucial factor for the concrete quality, the outstanding workability properties outweigh any disadvantages of SCC.
Based on this consideration, concepts are developed, how to bring about robust SCC cost-efficiently and reliably into practice as pre-mixed dry compound under consideration of local materials such as rice husk ashes, bagasse ashes, natural pozzolans, cassava starch and lignosulphonate.
Rwanda is a landlocked country in the East Africa. It is surrounded by Uganda, Tanzania, Congo and Burundi. Rwanda is a fast developing country and it spends most of its revenues to import fossil fuels from either through Mombasa Port in Kenya or Dar es Salaam port in Tanzania because the energy production in Rwanda is not sufficient for its development.
Transporting the fuels from these ports, add on to the cost of all materials, cement industry being no exception. There are three cement companies in Rwanda. The cement industries could not run in full production due to the shortage of fuel. Moreover, Rwanda is importing all the construction materials such as steel, roofing materials, etc from its neighbouring countries. This increases the cost of construction and the common man find difficult to own a house. In order to sustain the energy needs of Rwanda, different sources of energies should be focused. They are Peat, Geothermal, Methane gas, solar, wind, waste materials and Municipal wastes. Without affecting the environment, there is an urgent need to find a solution on sustainable energy in Rwanda. This paper discusses about the possible sources of energy in Rwanda which will improve the energy sustainability and turn the economy of Rwanda.
Portland cement, as we know it today, has its origin in Great Britain approximately 170 years ago. Since then, concrete technology has spread out to Europe, the United States, and Japan, where it became a key component for rapid industrial development. Europe, the Unites States and many Asian countries today have developed a high level of technology regarding concrete construction.
However, each of them has a unique history and as a result, different “concrete philosophy” depending upon the social, environmental and financial boundary conditions, as well as their evolution throughout the years and local construction traditions. As a result, the word concrete may refer to rather different materials in America, Europe, and Asia.
Apart from South Africa, most sub-Saharan African countries cannot look back on a similarly long cement and concrete history. Cement and concrete are rather new materials and not yet well established. This gives African engineers the unique opportunity to learn from past mistakes and to develop a concrete technology, which refers to the best available practice. However, in many sub-Saharan African countries, standards and regulations are adopted (preferably from Europe or the US) without consideration of the historical background of these standards. Although this practice helps saving resources for the implementation, it does not necessarily yield the best result in the African environment, and also from an economic point of view it might come back disadvantageously due to unnecessary overdesigning.
By comparing the differing states-of-the-art in North America, Europe, and Asia, this paper emphasizes, how regional conditions determine the practice of concrete technology in the sub-Saharan area. It is therefore important for Africa to develop a unique African concrete technology, which is perfectly fitted to the specific local conditions, even if it may vary distinctively from the established practice elsewhere. The paper concludes that African nations should effort into adapting existing principles that have proved to function well rather than adopting existing standards.