NICMAR – NICMAR – SODE SODE PGP-CM-MODULE-14
COURSE TITLE:
TECHNOLOGY AND MANAGEMENT OF HIGH RISE AND SPECIAL BUILDINGS COURSE CODE – CODE – PGCM42 PGCM42
PREPARED AND SUBMITTED BY:
NAME: MOHAMMED MOHAMMED NOMAN NOMAN REG NO: 215-06-11-50423-2171
TECHNOLOGY AND MANAGEMENT OF HIGH RISE AND SPECIAL BUILDINGS
ASSIGNMENT
Write a detail note on concreting for high rise buildings with regards to following points like: a) Slab cycle; its design and implementation. implementation. b) Various aspects and strategies related to CONCRETING at various heights. c) Use of batching plant, its significance. d) Concreting quality assurance and control etc.
High Rise Building: A building is an enclosed structure that has walls, floors, a roof and usually windows. “A „tall building‟ is a multi -story structure in which most occupants depend on
elevators to reach their destinations. The most prominent tall buildings are called „high-rise buildings‟ in most countries and „tower blocks‟ in Britain and some European countries. The terms do not have internationally agreed definitions.”
However, a high rise building can be defined as follows. “Any structure where the height of a building can have a serious impact on evacuation.” “For most purpo ses, the cut-off point for high-rise buildings b uildings is around seven stories.
Sometimes, seven stories or higher define de fine a high-rise, and a nd sometimes the definition is more than seven stories. Sometimes, the definition is stated in terms of linear height (feet or meters) rather than stories. “Generally, a high-rise structure is considered to be one that extends higher than the
maximum reach available fire-fighting equipment. In absolute numbers, nu mbers, this has been set variously between 75 feet (23 meters) and 100 feet (3 0 meters).” Or about seven to ten stories (depending on the slab-to-slab distance between floors). The exact height above which a particular building is deemed a high-rise is specified by fire and building codes for the country, region, state, or city where the building is located. When the building exceeds the specified spec ified height, then fire, an ever-present danger in such facilities, facilities, must be fought by fire personnel from inside the building rather than from outside using fire hoses and ladders.
For practicality and convenience such a multi-level or multi-story structure uses Elevators as a vertical transportation system and, in addition, some utilize escalators to move people between lower floors.
a) Slab Cycle; its design and implementation: implementation: Slab cycle is the amount a mount of time that is required between the casting of s labs, when we have got various var ious slabs to cast. Slab cycle involves various activities like marking, marking, shuttering of columns, reinforcement laying, casting, deshuttering, curing, curing, staircase reinforcement, staircase casting, casting, et cetera. The aim should be to optimally utilize our resources to keep this time minimum. The lesser the slab cycle time the faster our structure would get completed. b) Various aspects and strategies related to CONCRETING at various heights: Concrete is the most versatile, effective and a nd main component of any construction. The challenge to pouring of concrete c oncrete arises when it is conveyed c onveyed from heights. It requires i. High Performance Concrete (HPC): The strength of the high performance concrete ranges from 50 Mpa – 100 Mpa Requirements:
Very low water / cement ratio generally less than 0.3
Considerably high cement content
Part of cement is replaced by cementitious materials
Use of high efficient superplasticizers
Challenges for making high performance Concrete:
Variations in fine and coarse aggregates
Different source of cement with varying mineralogy
Different cementitious material properties
Varying climatic conditions
ii. Conveying (pumping) concrete to the required height: Because of very low low water / cement ratio and high high fines content, the the concrete becomes very sticky, very viscous and difficult to pump. Sika viscocrete (superplasticizer) technology helps in reducing the viscosity,
yield stress, giving better fresh concrete behaviour even at such low water / binder ratio so that concrete can be pumped easily to the required height. iii. Workability over time: To bring the concrete from long distances or site batched concrete. co ncrete. the concrete should have minimum flow retention period of 2-3 hours for pumping and finishing finishing and it should set normally . sika viscocrete viscocrete technology helps in retaining workability for hours without w ithout any effect on the setting time of the concrete. c) Use of batching plant, its significance: Construction of high rise buildings requires huge amounts of concrete. There is always a need of o f central mixing plant with storage bins of adequate adeq uate capacities for the production of concrete in such huge amounts. The plant must be accessible for transportation for both ingredients for batching batc hing and placing of concrete produced at the the desired location. The batching plant comprises
Storage bins
Weigh hoppers
A central plant mixer
A plant that has a central c entral plant mixer is referred to as a central mix plant. The ingredients like aggregates, cement, ce ment, water and admixtures need to be delivered to the batching plant directly or stored for later transfer to the plants storage bins. The ingredients ingredients are delivered to the mixer after after batching. Aggregates can be delivered to the storage bins if conveying system syste m is readily available for the purpose. Cement Ce ment is transferred to watertight silos / bins by pneumatic pumping or by using screw conveyor or bucket elevator. Water and liquid admixtures may be pumped pu mped to storage vessels. The storage bins are available in almost almost all conceivable size and shape. The increasing development in urban centres has prompted the demand for a suitable concrete batching plant. A concrete batching plant is a device that
mixes various ingredients to form concrete. The plants are used in various projects like construction construction of roads, bridges, and buildings. buildings. Urban areas are the hub of various activiti act ivities es thus will w ill experience developments in real estate and infrastructure. Middle-east is among the fastest growing regions and has experienced increased demand for concrete. co ncrete. Concrete batching plants are easy to transport from on site s ite to another and the installation and setup time is minimal. Earlier the traditional plants had to be setup se tup near the source of raw materials. The modern batching plants have offered flexibility in the site location. The batch plant can be setup in the th e area where it will serve a town and the surrounding environments where traffic congestion results to higher delivery costs. There are also situations s ituations where a plant needs to increase its productivity capacity due due to a limited timeline timeline of completion of the the project, the plant can be easily relocated. The plant has also reduced accidents which are mainly caused by operator errors. Importance:
High quality concrete is produced due to the accuracy in measuring and mixing the ingredients.
The batching plant located at the construction site saves transportation time and risk of delays which will in turn save costs.
Due to congestion in urban areas which makes some construction sites unreachable, a concrete pump enables conveyance co nveyance of concrete. Also in areas where there are weight and access restrictions the concrete pump p ump offers versatility where concrete id poured to a site by a concrete pump.
Small construction sites that require a small s mall quantity of cement, they can have a mobile mobile batching plant near the construction site. After the concrete is ready it can be transported to the site s ite by a truck.
Demolished concrete from a dismantled site is limited, a compact batching plant occupies little little space at a site in addition to being very very
easy to maintain. Also due to limited space for raw materials storage makes it the most viable option.
Batching plants are automated to mix the ingredients evenly and quickly resulting to high efficiency. It also increases production capacity.
Apart from relevant authorities the batching plant requires no prior planning. The concrete pump pump is set up immediately.
Construction sites have a large number of casual workers. The batch plants will reduce the the labor costs since it comes comes with an automated mixers and loaders.
The same quality and standard of o f concrete is maintained maintained on every mix since it maintains the same mixing ratio and a nd uniformly mixes the ingredients.
d) Concreting quality assurance and control etc: Quality Assurance: It is defined traditionally as “all those planned and systematic actions necessary to provide adequate confidence that t hat a structure , a system or a component will render or perform safe and trouble-free trouble- free services and satisfy specified requirements.” QA is a management tool. The
owners or their representatives are responsible for quality assurance. Quality assurance is a part of quality management focused on providing confidence in fulfilling the quality requirements. Quality Control: It is traditionally defined as “those QA actions required to keep control and regulate factors to attain predetermined qualitative ials, processes processes and services.” Executing characteristics related to mater ials,
agencies use operational techniques and activities to fulfil the requirements for quality. As rectification of unsatisfactory work would escalate cost and delay the progress of construction activities, executing agencies need to pay utmost attention to quality so as to avoid subsequent rectification/reworking. rectification/reworking. QC is a production tool. QC is a part of quality management and is focused
on fulfilling quality requirements to attain predetermined qualitative characteristics related to materials, processes and services. Importance properties of concrete:
Workability Non-segregating Setting in specified time
The essential properties of hardened concrete:
Strength
Water-tightness
Durability
Volume stability
Abrasion resistance
Economy
Quality of fine and coarse aggregates: Aggregates form the bulk of the volume of concrete about 60% to 75% of o f total volume and by far the largest amount of aggregates used in concrete is mineral aggregates such as gravels, crushed stones and stones. Aggregates are inert materials. Their physical, thermal and chemical properties may influence the performance of the concrete. They should be free from substances such s uch as iron pyrites, coal, mica and organic impurities which affect hydration o f cement and durability of concrete. Aggregates are classified into two groups:
Fine aggregates passing through the 4.75mm 4.75 mm sieve and within the grading limits.
Coarse aggregates retained by the 4.75 mm sieve ranging up to 150mm.
Next to water-cement ratio, it it is the aggregates that have have the most significant effect on the workability workability of concrete. This is primarily a function of the surface area of aggregates in a given volume of concrete and consequently of the demand of mixing water that aggregates create. The lower the surface area of the aggregates, the lower is the demand for mixing water for a given workability. Conversely, if the water co ntent of a mix is fixed, as it normally is from the consideration of strength, workability will increase when:
Maximum size of aggregates is increased
A coarser overall grading grading of the aggregates is available available as the ratio ratio of coarse to fine aggregates increases
The particle shape approaches a sphere – the the rounded particles increases workability most, followed by irregular o nes, then by angular ones and finally by flaky and elongated ones
The surface texture of the aggregates becomes smoother
Quality of water: The function of water, the active component of concrete, is two fold:
To react with cement chemically (hydration) to form a cement gel wherein the aggregates remain in suspension s uspension till hardening of cement paste
To serve as lubricant between fine and coarse aggregates so that the concrete may be easily placed and compacted co mpacted – to to make concrete workable for specific use.
Water that is to be used in concrete shall be clean and free from such impurities as suspended solids, organic matter and dissolved disso lved salts which are frequently contained in natural water and which may adversely affect the properties of concrete, especially es pecially setting and hardening. Water should for the same reason be free from injurious oils, acids, alkalis, organic
matters, salts, silts or other deleterious impurities. impurities. Mixing water for concrete is required to be fit for drinking or to be taken from a n approved source. The sources of satisfactory water can be lakes, streams or wells, groundwater. Use of admixtures: Admixtures are added to concrete to change its properties. Types of admixtures: Chemical: a. Water reducers: They decrease the water requirement for a concrete mix and cement content is decreased without loss of strength. Super plasticizers are example example of high range water reducer. b. Set Accelerators: these are used to decrease the time from the start s tart of addition of water to cement to initial set and to increase the rate of strength gain of concrete. Calcium chloride is a type of set accelerator but b ut it corrodes steel. c. Set retarders: They delay de lay the initial set of concrete. Water reducers to some extent are set retarders. The initial set is delayed for several hours to several days. They increase the compressive strength of concrete d. Air entraining admixtures: these are used to create air bubbles in the concrete intentionally to protect it from freezing and thawing. It creates less bleeding and less corrosion. Bibliography/references:
Textbook of construction technology
