Considerable bad experience has been encountered when alkali reactive aggregates have been used.Low alkali cement is normally required to protect against disruptive
Expansion of concrete which occurs generally due to alkali-aggregate reaction.(a chemical reaction between alkali’s in the cement and reactive aggregates.Another means of of controlling alkali-aggregate reactions is by the use of suitable fly ash or natural pozzolan.If a highly reactive aggregate have to be used then it is necessary to use a low alkali cement and a pozzolan.
Another design recommendation is the type of the cement to be used.Type-2 cement is normally used by the Bureau of Reclamation in mass concrete dams.Limitations on the
Heat of hydration of this cement are specified when determined necessary to minimize cracking in the concrete structure.Use of Type-2 cement will generally reduce the heat of hydration of cement to an acceptable level, particularly when type-2 cement is used in conjunction with other methods of heat reduction.These include use of lower cement content and using pozzolan as part of the cementitious material,use of pipe cooling system and use of a specified maximum temperature for placing of concrete,which may be as low as 50 degF.Use of all or some of this methods usually reduce or eliminate the need for stringent limitations on heat of hydration of concrete.However a limitation of 58% on Tricalcium Aluminate plus Tricalcium Silicate content of Type-2 required where
Heat of hydration must be kept low.Further limitation on heat of hydration,if more stringent control of heat is needed can be obtained with a Type-2 cement by providing a maximum limitation on the cement of 70 calories per gram at 7 days or 80 calories per gram at 28...
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Conveying concrete whose aggregate size is less than 7.5 cm.Pumping of concrete is to be done in such way that concrete without air pockets or interruptions is delivered.
Placing of Concrete:
Concrete has to be placed at a uniform rate through out the placing of the concrete.
Each layer is compacted well before placing of the other layer.Generally thickness of layers shall not exceed the following limits.
Reinforced Concrete-25 cm.
Vibrated Concrete-45 cm.
Hand compacted mass concrete-30 cm.
Concrete is placed vertically above the other layer so as to avoid damage,segregation and air pockets.Compaction should be done as quickly as possible after placing.When concrete is placed in the forms temperature may go high as suggested by some previous studies so measures have to be taken in order to reduce such effects.They are
Investigating Factors that Affect the Rate of Reaction Between marble and Dilute Hydrochloric Acid The local Council are concerned about the effect of acid rain on the marble statues in the local park. Investigate a factor that affects the rate of reaction between marble (calcium carbonate) and dilute hydrochloric acid. There are three main factors that affect the rate of reaction. These are: Particle size Concentration Temperature With investigating any of these, there are slight problems which make them not as reliable as they could be. With particle size, it is extremely difficult to get control of the sizes, e.g. large, small, medium.
In this experiment, solid calcium nitrate, solid diammonium hydrogen phosphate, and aqueous ammonia are used to form calcium hydroxyapatite.
Besides the known inventions and renovations of the Roman Empire, one of the building materials that the Roman Empire produced was concrete. With its strength, inexpensiveness and its easiness to work, the Roman Empire left an everlasting impact. Concrete that is a mixture of aggregate, which is usually gravel, sand or small stones, binding agents, and water is used to construct buildings and infrastructure. The first one, aggregate, gives the product its mass while the second one, binding agents, is used to harden the product. In the early times of the history, limestone powder was usually used as a binding agent in the mixture. The Romans later used “pulvis puteolanus” (pozzolanic ash), which was a fine volcanic ash as a binding agent and it allowed Romans to have strong concrete that is also durable (Yegeul, n.d.). It was easy to use
Investigation into the Reaction Between Marble Chips and Hydrochloric Acid Planning = == == == =
-Selection of solvent – The correct solvent must be selected to form a product of high purity and in good recovery. The solvent must fit some criteria. The desired compound should be soluble in the hot solvent but insoluble in the cold solvent. The impurities should be insoluble in all temperatures of the solvent or slightly soluble in a cold solvent. The boiling point of the solvent should be low enough to remove the crystals. The solvent should not react chemically with the solids that are being purified. The solvent needs to have a boiling point lower than the melting point of the solids.
Whether you are responsible for a major thoroughfare, commercial parking lot or residential driveway featuring asphalt pavement, you have probably heard that timely crack repairs can extend the life of your pavement. Cracks that are left open to the elements allow water to penetrate to the pavement's supporting foundation. The foundation becomes unstable and incapable of bearing the weight of the pavement, frequently leading to widespread damage that can only be remedied by replacing the pavement. However, you may not know whether to choose a hot-pour or cold-pour sealant when you ask a contractor to repair the cracks in your pavement. An overview of the differences between the two types of sealants can help you make the best choice for your
acids. I only tried the 1 molar acid, but if I were to repeat the
Cooling allows the plastic to solidify and become dimensionally stable before ejection. Heat that has been transferred to the mould by the molten plastic is carried away by a coolant that circulates through cored passages in the mould. Coolant temperature and flow rate determines the efficiency of heat removal. Cooling the moulded components uniformly may mean either, cooling the mould with different flow rates of cooling medium in different areas or, using the same flow rate throughout the mould but with different temperatures of cooling medium. The objective is to cool the components as quickly and as uniformly as possible, while ensuring that defects such as poor surface finish and changes in physical properties are not
[17] BS 4550-3.4:1978. Methods of testing cement, Physical tests, Strength tests. British Standards Institution ; 2007.
In this report, we will introduce and illustrate on precast concrete, pre-stressed concrete, ready-mix concrete, reinforced concrete, terrazzo and Urbanite in details.
For the case undertaken in this thesis work, the result we got according to the given options by the management of Lafarge Surma Cement Ltd. Indicates that, distributor storage with last mile delivery is the best choice of the distribution network. It is followed by retail storage with customer pick up and Manufacturer/Distributor storage with customer pickup. The selected network is tailored to match the characteristics of the product and the performance along with the needs of the customer. From the analysis, it is a suitable option for fast moving items for which some level of aggregation is beneficial. In this network, warehouse is much closer to the end customer and there is a requirement of high number of warehouses than other options.
Concrete, a crucial material in building construction, is the world’s most produced material. However, the production of Portland cement, an essential ingredient of concrete, involves energy intensive processes, which leads to significant amounts of CO2 emissions (calcium carbonate + heat = calcium oxide + carbon dioxide) (Ecocem, 2001). The global cement industry is responsible for around 7 per cent of all CO2 emissions and around 4 per cent of global warming (Ecocem, 2001). Each year, approximately one ton of concrete is placed for every man, women and child (West, 2013). To date, approximately 7.2 Billion people inhabit the planet, with a projected population of around 9 Billion for 2040 (CSO, 2013). Therefore, global placement of concrete is around 7.2 Billion tons with a projected usage of 9 Billion tons. Such vast amounts of concrete require vast amounts of natural resources for aggregate and cement production.
[A]Cement [B] Cement paste [C] Cement paste & Fine aggregates [D] Mortar & Coarse aggregates.
Cement : Cement should develop appropriate strength. The Ordinary Portland Cement of 53 grades conforming to IS: 8112 is being used.
The porous structure of natural zeolite enable to holds water which can increase curing time and increase strength during curing. Zeolites also have much higher cation exchange capacities than other natural pozzolans in which prevents the alkali-silica reaction.