Darbas:
are added during the mixing process. Some admixtures add fluidity to concrete while requiring less water to be used. An example of an admixture which affects strength is superplasticizer. This makes concrete more workable or fluid without adding excess water. A list of some other admixtures and their functions is given below. Note that not all admixtures increase concrete strength. The selection and use of an admixture are based on the need of the concrete user.Hoover Dam (4,360,000 cubic yards of concrete)
Photo Courtesy of the US Department of the Interior
Properties of Concrete
Concrete has many properties that make it a popular construction material. The correct proportion of ingredients, placement, and curing are needed in order for these properties to be optimal.
Good-quality concrete has many advantages that add to its popularity. First, it is economical when ingredients are readily available. Concrete's long life and relatively low maintenance requirements increase its economic benefits. Concrete is not as likely to rot, corrode, or decay as other building materials. Concrete has the ability to be molded or cast into almost any desired shape. Building of the molds and casting can occur on the work-site which reduces costs.
Concrete is a non-combustible material which makes it fire-safe and able withstand high temperatures. It is resistant to wind, water, rodents, and insects. Hence, concrete is
Concrete does have some limitations despite its numerous advantages. Concrete has a relatively low tensile strength (compared to other building materials), low ductility, low strength-to-weight ratio, and is susceptible to cracking. Concrete remains the material of choice for many applications regardless of these limitations.
The compressive strength of concrete is usually at least ten times its tensile strength, and five to six times its flexural strength. The principal factors governing compressive strength are given below:
• Water-cement ratio is by far the most important factor.
• The age of the cured concrete is also important. Concrete gradually builds strength after mixing due to the chemical interaction between the cement and the water. It is normally tested for its 28 day strength, but the strength of the concrete may continue to increase for a year after mixing.
• Character of the cement, curing conditions, moisture, and temperature. The greater the period of moist storage (100% humidity) and the higher the temperature, the greater the strength at any given age.
• Air entrainment, the introduction of very small air voids into the concrete mix, serves to greatly increase the final product's resistance to cracking from freezing-thawing cycles. Most outdoor structures today employ this technique.
In conclusion I would like to say that concrete is very beneficial building material. All builders and all construction enterprises use it. Concrete is durable building material, so buildings made from it are lasting and these buildings does not need reconstruction for long time.
Keywords:
treatment – apdirbimas
consolidation – sutvirtinimas
durability – patvarumas
compound material – sujungta medžiaga
hydrate – hidratas
binding – jungimas
embed – įstatyti
reinforcement – sustiprinimas
expansion – plėtimasis
spalling – nuolauža
bar – gabalas, luitas
rough – šiurkštus
chipping – skalda
compound – mišinys
intermittently – nenutrūkstamai
a lattice – grotelės
tension – įtempimas
flexure – lenkimas
thermal – šiluminis
expansion – plėtimasis
molten – išlyditas
clinker – šlakas
powder – milteliai
investigator – tyrinėtojas
alkalinity – šarmingumas
matrix – rišamoji medžiaga
consolidate – sutvirtinti
weaker – silpnesnis
porosity – poringumas
fluidity – skysta busena
admixture – įmaišymas
corrode – korozijos veikimas
decay – puvimas
ductility - elastingumas
lasting – patvarus, ilgalaikis
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