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Proportioning
The key to achieving a strong, durable concrete rests in the careful proportioning and mixing of the ingredients. A mixture that does not have enough paste to fill all the voids between the aggregates will be difficult to place and will produce rough surfaces and porous concrete. A mixture with an excess of cement paste will be easy to place and will produce a smooth surface; however, the resulting concrete is not cost-effective and can more easily crack.
Portland cement's chemistry comes to life in the presence of water. Cement and water form a paste that coats each particle of stone and sand—the aggregates. Through a chemical reaction called hydration, the cement paste hardens and gains strength.
The quality of the paste determines the character of the concrete. The strength of the paste, in turn, depends on the ratio of water to cement. The water-cement ratio is the weight of the mixing water divided by the weight of the cement. High-quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete, allowing it to be properly placed, consolidated, and cured.
Portland cement's chemistry comes to life in the presence of water. Cement and water form a paste that coats each particle of stone and sand—the aggregates. Through a chemical reaction called hydration, the cement paste hardens and gains strength.
The quality of the paste determines the character of the concrete. The strength of the paste, in turn, depends on the ratio of water to cement. The water-cement ratio is the weight of the mixing water divided by the weight of the cement. High-quality concrete is produced by lowering the water-cement ratio as much as possible without sacrificing the workability of fresh concrete, allowing it to be properly placed, consolidated, and cured.
Almost any natural water that is drinkable and has no pronounced taste or odor may be used as mixing water for concrete. Excessive impurities in mixing water not only may affect setting time and concrete strength, but can also cause efflorescence, staining, corrosion of reinforcement, volume instability, and reduced durability. Concrete mixture specifications usually set limits on chlorides, sulfates, alkalis, and solids in mixing water unless tests can be performed to determine the effect the impurity has on the final concrete.
Although most drinking water is suitable for mixing concrete, aggregates are chosen carefully. Aggregates comprise 60 to 75 percent of the total volume of concrete. The type and size of aggregate used depends on the thickness and purpose of the final concrete product
Although most drinking water is suitable for mixing concrete, aggregates are chosen carefully. Aggregates comprise 60 to 75 percent of the total volume of concrete. The type and size of aggregate used depends on the thickness and purpose of the final concrete product
Relatively thin building sections call for small coarse aggregate, though aggregates up to six inches in diameter have been used in large dams. A continuous gradation of particle sizes is desirable for efficient use of the paste. In addition, aggregates should be clean and free from any matter that might affect the quality of the concrete.
Hydration Begins
Soon after the aggregates, water, and the cement are combined, the mixture starts to harden. All portland cements are hydraulic cements that set and harden through a chemical reaction with water call hydration. During this reaction, a node forms on the surface of each cement particle. The node grows and expands until it links up with nodes from other cement particles or adheres to adjacent aggregates.
Once the concrete is thoroughly mixed and workable it should be placed in forms before the mixture becomes too stiff.
During placement, the concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycombs and air pockets.
Once the concrete is thoroughly mixed and workable it should be placed in forms before the mixture becomes too stiff.
During placement, the concrete is consolidated to compact it within the forms and to eliminate potential flaws, such as honeycombs and air pockets.
For slabs, concrete is left to stand until the surface moisture film disappears, then a wood or metal handfloat is used to smooth off the concrete. Floating produces a relatively even, but slightly rough, texture that has good slip resistance and is frequently used as a final finish for exterior slabs. If a smooth, hard, dense surface is required, floating is followed by steel troweling.
Ergonomy
Ergonomics comes from the Greek
words for work (ergon) and law (nomos) and can be interpreted as "a study
of the laws of work." However, we generally think of ergonomics in the workplace
as the science of designing work to fit the capabilities of workers, thereby
enhancing worker well being.
Some people call ergonomics human
factors engineering. Let's look at an analogy with machinery. If a new machine
is installed in a plant, the responsible engineer will read all the
specifications in the manual that comes with the machine, including operating
and maintenance information, before beginning to operate it. But how about
workers? What are their "specs?" Actually, years of ergonomics
research have resulted in a database that can provide "spec sheets"
on performance of joints and other aspects of human anatomy. This type of data
should be used in designing work, so as to protect the investment in human
capital at least as much as is regularly done for investments in equipment.
OSHA states that one third of all
recordable worker injuries each year result from ergonomic hazards. Such
injuries include upper extremity disorders, often associated with lifting and
repetitive motion, which are on the rise every year. OSHA has estimated the
cost of ergonomic injuries to amount to $15 billion per year.
Obviously workplace injuries are
costly to business, in the form of lost time, worker compensation claims,
reduced productivity, and adverse effects on product quality. Whether good
ergonomic practices are mandated by government or not, they should be mandated
by good business sense, because they pay off.
Most of the chemicals produced and used today are beneficial, but some also have the potential to damage human health, the environment, and public toward chemical enterprises. You must be aware of the potential for the accidental misuse of chemicals, as well as their intentional misuse. Chemical safety and security can mitigate these risks.
A new culture of safety and security consciousness, accountability, organization,
and education has developed around the world in the laboratories of the chemical
industry, government, and academe. Chemical laboratories have developed special
procedures and equipment for handling and managing chemicals safely and securely.
The development of a “culture of safety and security” results in laboratories
that are safe and healthy environments in which to teach, learn, and work.
WHAT ARE THE TYPES OF HAZARDS AND RISKS?
- Large-Scale Emergencies and Sensitive Situations
- Security Breach
- Toxic Chemical Exposure
- Flammable, Explosive, and Reactive Chemicals
- Biohazards
- Hazardous Waste
- Physical Dangers
TEN STEPS TO ESTABLISH A SAFETY AND SECURITY
MANAGEMENT SYSTEM
- Create an Institutional Safety and Security Oversight Committee and Appoint a Chemical Safety and Security Officer (CSSO).
- Develop a safety and security policy statement.
- Implement administrative controls.
- Identify and address particularly hazardous situations.
- Evaluate facilities and address weaknesses.
- Establish procedures for chemical management.
- Employ engineering controls and personal protective equipment.
- Plan for emergencies.
- Identify and address barriers to following safety and security best practices.
- Train, communicate, and mentor.
ISO is an independent,
non-governmental international organization with a membership of 165 national standards
bodies. The International Standards provide solutions to global challenges. ISO
will make every effort to be attractive and responsive to the needs of
industry, as well as those of regulators, consumers and other stakeholders.
In particular, the Strategy will
help the organization respond to a future where:
·
Technological, economic, legal, environmental,
social and political challenges will require examination and continual
improvement of the ISO system.
·
Stakeholder engagement and the challenges to
ISO’s intellectual property will continue to be both a key opportunity and risk
for ISO
v Develop high-quality standards through ISO’s global membership.
The organization must both excel
in the core business of developing standards which includes applying good standardization
practices such as those established by the World Trade Organization and ensure
it makes the most of its valuable network of national members.
v Engage stakeholders and partners.
Effective and wide-reaching
stakeholder engagement is essential in order to maintain ISO’s credibility and
the relevance of International Standards. This means ensuring that all ISO members
can successfully drive stakeholder participation in addition to effectively
engaging with global and regional partners. Stakeholders must see their
national members as the pathway to ISO, as organizations that engage them on
important issues with other national stakeholders and connect them to the
global standards debate. ISO needs to clearly show its value to stakeholders.
v People and organization development.
ISO’s most important resource is
its member organizations and their networks of experts. ISO will therefore
invest in building the capacity of all its members, both at the human and the
organizational level, through learning, research and development solutions.
This includes supporting the transfer of knowledge to a younger generation of
experts.
v Use of technology.
Cutting-edge technology, shifting
demographics, changing social behaviours and new collaborative work practices
are creating new demands and possibilities for all organizations. It also challenges traditional notions of how
we consume and use information; of pub- lishing and copyright. The impacts of
these changes are particularly profound for global, information-based
businesses such as ISO.
v Communication.
The value and impact of International Standards
must be recognized by decision makers in both the public and private sector, as
well as by all stakeholders and the general public. The ISO member network,
supported by ISO’s Central Secretariat, is key to fulfilling this aspiration.
Beyond their role as national standards bodies, ISO members “ are ” ISO in
their country and are the driving force for communicating with the various
groups interested in, and affected by, standards.
Petroleum Processing
The term petroleum comes from the Latin stems petra, “rock,” and oleum, “oil.” It
is used to describe a broad range of hydrocarbons that are found as gases, liquids,
or solids beneath the surface of the earth.
The two most common forms are natural
gas and crude oil.
Natural gas: Natural gas which is a mixture of lightweight alkanes, accumulates in
porous rocks. A typical sample of natural gas when it is collected at its source contains
about 80% methane (CH4
), 7% ethane (C2
H6
), 6% propane (C3
H8
), 4% butane and
isobutane (C4
H10), and 3% pentanes (C5
H12). The C3
, C4
, and C5
hydrocarbons are
removed before the gas is sold.
The commercial natural gas delivered to the customer
is therefore primarily a mixture of methane and ethane. The propane and butanes
removed from natural gas are usually liquefied under pressure and sold as liquefied
petroleum gases (LPG).
Crude oil is a composite mixture of hydrocarbons (50-95% by weight) occurring
naturally. The first step in refining crude oil involves separating the oil into different
hydrocarbon fractions by distillation. Each fraction is a complex mixture.
For example,
more than 500 different hydrocarbons can be found in the gasoline fraction.
Petroleum is found in many parts of the world which include the Middle East, southern
United States, Mexico, Nigeria and the former Soviet Union.
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