2.0 INTRODUCTION TO CURING
Curing is basically a process that controls the rate and extent of moisture lost in a concrete during the operation of cement hydration. A concrete takes a period of time (hours, days, weeks) depending on the types of concrete used in order for it to reach its potential strength and durability. Henceforth, the process of curing is needed.
Besides that, there are also a few factors that affecting the curing period, depending on the types of concrete used. For instance, the temperature and the humidity of the atmosphere are dependent on the duration for the concrete to cure.
To be more precise, the main purpose of curing is actually to retain the saturation of the concrete. This is because the uncured cement paste
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It must be taken care of to avoid damages or torn of the plastic sheeting. The minimum thickness of sheet is normally 0.01mm so that it would not be able to be torn easily. Appropriate color of the sheet also carries a vital role for ambient condition. In general, plastic sheet with dark or dim color will absorb heat faster which is unsuitable for concrete but it is beneficial in accelerating the rate of hydration in a cold weather. In contrast, white or lightly colored sheets are often used for when the weather is hot as it helps to reflect the ultraviolet rays from the …show more content…
The concrete should go through a pre-set time that is recommended for two to three hours. Then, a period of time needed to increase the curing-cell temperatures to target temperature which known as ramp time. If temperature exceeds 22 oC/ hour, cracking might occurred due to thermal shock. To avoid delayed ettringite formation (DEF), ambient curing temperature shall not go beyond 65 oC.
The concretes are placed inside a room or chamber for steam curing. Basically, the heat and moisture will penetrate at the very fast rate to ensure hydration occurred entirely. Operator is able to regulate the appropriate temperature, humidity and pressure level by using a control panel. Compare to outdoor curing, it will be much challenging as it is impossible to control these factors. Therefore, the whole process is usually supervised and lesser time needed to harden the concrete. However, the concrete might become weaker in the long run. Minor issues such as crumbling are more likely to develop using steam curing. One day, these minor problems would slowly turn into major predicaments if no action were
But in order to completely seal off the RC a restoration is placed onto the treated RC. This will completely off the RC from the outside environment and prevent wear and abrasion of the RC
In this report, we will introduce and illustrate on precast concrete, pre-stressed concrete, ready-mix concrete, reinforced concrete, terrazzo and Urbanite in details.
Then the mould is removed by lifting it slowly and carefully in a vertical direction. This allows the concrete to subside. This subsidence is referred as slump of concrete.
High pressure kiln pressure (autoclave) –temperature is generally higher about 300-375 F and pressure is 80-185 psi block is left to soak for 10 hours , pressure is then decreased rapidly , because of which trapped moisture of block is released quickly. It is more costly process but it takes less time.
It decreases the chances for caking of partially hygroscopic materials, in case of storage as a powder. This is achieved since the moisture is adsorbed onto the surface of the granulated particles and they can still maintain their flowability due to its size(1).
During hydration the cement reacts with the water to form three main components; calcium hydroxide (Ca(OH)2), Calcium Silicate hydrate (C-S-H), and aluminum trisulfate also known as ettringite [4]. The C-S-H forms a gel that accounts for around 50% of the paste and is where most of the strength of the cement comes from by becoming a binding phase for all of the crystal structures formed in the cement paste. Calcium hydroxide then accounts for around 15 % of the cement paste and forms uneven hexagonal crystals that are grown around the C-S-H. Ettringite along with other products of the C₃A and C₄AF reactions account for 15- 25% of the paste form more crystalline parts of the paste the do not provide much to the strength of the cement
High pressure processing can be performed in variety of different ways including high pressure pasteurization (destruction of all pathogenic microorganisms) and high pressure sterilization (removal of all microorganisms).
2.1 Introduction In a traditional way, a concrete mix is designed based on the code requirements and recommendations, which uses the empirical values obtained from previous experiences. Compressive strength of concrete is determined by conducting standard uniaxial compression test on standard cylindrical sample specimens of ages 7 & 28 days, following the standard procedure and test values are reported in accordance with ASTM and ACI standards. If the strength value obtained from the test is less than the required strength after 28 days from date of placing of concrete, the entire process of concrete mix design has to be repeated until the required strength value is achieved, which is time consuming and costly. Numerous test samples with different mix ingredient proportions have to be created to achieve the required strength, and this is an iterative process. So, every mix designer wants a tool or methodology to predict the compressive strength of concrete required at the time of design, before placing the concrete.
The dry ingredients are supplied through the hopper and drops down to barrel with or without preconditioning (depend on the specifications of final product). The food is moved forward with the help of the augur. This augur has flights on it and the pitch decreases with increase in length of the screw. As we move ahead, the diameter of the augur is increased and furthermore, the space for the food is reduced which in turn results in higher compression, pressure and temperature. Since the food is being compressed, mechanical energy is dissipated and there is also an option to provide external thermal energy. Though, the manufacturers may not use the external energy provided the pre-set conditions can be achieved by the dissipation of mechanical energy, shear and the friction developed. When the food emerges out of the extruder from high pressure and temperature (generally above 100ᵒC) to relatively low pressure and temperature (room temperature), the moisture is whizzed off as steam resulting in the expansion of the final product (GangulyS., 2014). The expansion of extruded food product majorly depends upon the difference between the vapour pressure of water and the pressure just outside the extruder that is the atmospheric pressure along with the capability of expanding of that particular food stuff (SinghR.K.R.,
This project entailed subjecting the designed concrete mixes to a series of tests to evaluate the strength, and other properties. For this project, it was important to monitor the strength development with time to adequately evaluate the strength of each concrete mix. For each test, either 3 samples from each mix were tested at each curing age, and the average values were used for analysis. The following sections present the procedures used for the various tests.
The simultaneous heat and mass transfer to changes the temperature of the wet solid to evaporate its surface moisture and the transfer of moisture to the surface of the solid for subsequent evaporation from the surface to the surrounding atmosphere take place during drying processes. Normally, the hot air or combustion gases surrounding the feed are the drying medium. The psychrometry and the use of humidity charts determine the actual quantities of air required to remove the moisture liberated by evaporation. During heat transfer to a wet solid, the temperature Gradient developed within the solid and the moisture evaporation from the surface become the driving force for migration of moisture from within the solid to the surface, which occurs through diffusion, capillary flow, internal pressures due to the shrinkage during drying, and repeated and progressive vaporization and re-condensation of moisture to the exposed surface in the case of conduction type indirect drying. An appreciation of this internal movement of moisture is important when it is the controlling factor, as it occurs after the critical moisture content, in a drying
Cement is a finely ground powder binder, a material that sets and hardens and can bind other materials together, when mixed with water it forms a hardening paste of calcium silicate hydrates and calcium aluminates hydrates. it evokes highly diverse reactions. Cement is used in mortar (a combination of sand and roughly burnt gypsum) and concrete (bulk rock-like building material made from aggregate, sand, and water). By modifying the raw material mix and the temperatures utilized in manufacturing, compositional variations can be achieved to produce cements with different qualifications. Cement, chemically speaking, is a product including lime as the primary ingredient, but it is far from the first material used for cementation. The Babylonians and Assyrians used bitumen to bind together burnt brick or alabaster
Wood is a biological material that, when in the tree, contains large amounts of water. As wood dries to a moisture content (MC) in equilibrium with its in-use environment, many of its properties and characteristics change.
Almost every industrial company has at least two compressors, and in a medium-sized plant there may be hundreds of different uses of compressed air. Uses include powering pneumatic tools, packaging and automation equipment, and conveyors. Pneumatic tools tend to be smaller, lighter, and more navigable than electric motor-driven tools. They also distribute smooth power and are not damaged by overloading. Air-powered tools have the capability for a lot of variable speed and torque control, and can reach a preferred speed and torque very quickly. In addition, they are often selected for safety reasons because they do not produce sparks and have low heat build-up [3]. Although they have many advantages, pneumatic tools are generally much less energy-efficient than electric tools. Many manufacturing industries also use compressed air and gas for combustion and process operations such as oxidation, fractionation, cryogenics, refrigeration, filtration, dehydration, and aeration. Compressed air also plays a significant role in many non-manufacturing sectors, including the transportation, construction, mining, agriculture, recreation, and service
In the most general sense of the word, concrete is a substance that solidifies to act as glue. Romans were the first to use “modern cement “for purposes of masonry made of crushed stone with vivid lime as binder. They named this substance “caementicium opus”, which was later referred to as cement, cimentim, cäment and cement. Cement is mainly used in construction. It is a gray powdery substance that burns lime and clay, mixed with water and sand to make mortar (a paste used to bind the building blocks together and fill the spaces between them) or with water, sand and gravel to make concrete (a strong, durable construction material).