MATERIALS - CONCRETE Flashcards
Typ Design strength Of Concrete
2000 psi, 3000 psi (most common) and 4000 psi, higher strength up to 12.000 psi are available
CURING Time Of Concrete
Gains 70% of strength in first week,
Deign STRENGTH IN 28 DAYS
(7 FOR EARLY-STRENGTH CONCRETE)
CEMENT TYPE I
GENERAL CONSTRUCTION
Type I is a general purpose portland cement suitable for all uses where the special properties of other types are not required. It is used where cement or concrete is not subject to specific exposures, such as sulfate attack from soil or water, or to an objectionable temperature rise due to heat generated by hydration. Its uses include pavements and sidewalks, reinforced concrete buildings, bridges, railway structures, tanks, reservoirs, culverts, sewers, water pipes and masonry units
CEMENT TYPE II
RESISTANT TO MODERATE SULFATE ACTION , MODERATE HEAT BUILD-UP
used where precaution against moderate sulfate attack is important, as in drainage structures where sulfate concentrations in groundwaters are higher than normal but not unusually severe (Table 2). Type II cement will usually generate less heat at a slower rate than Type I. With this moderate heat of hydration (an optional requirement), Type II cement can be used in structures of considerable mass, such as large piers, heavy abutments, and heavy retaining walls. Its use will reduce temperature rise – especially important when the concrete is placed in warm weather.
CEMENT TYPE III
HIGH EARLY STRENGTH
provides high strengths at an early period, usually a week or less. It is used when forms are to be removed as soon as possible, or when the structure must be put into service quickly. In cold weather, its use permits a reduction in the controlled curing period. Although richer mixtures of Type I cement can be used to gain high early strength, Type III, high- early-strength portland cement, may provide it more satisfactorily and more economically.
CEMENT TYPE IV
LOW HEAT
low heat of hydration cement for use where the rate and amount of heat generated must be minimized. It develops strength at a slower rate than Type I cement. Type IV portland cement is intended for use in massive concrete structures, such as large gravity dams, where the temperature rise resulting from heat generated during curing is a critical factor.
CEMENT TYPE V
SEVERE SULFATE RESISTANCE
Type V is a sulfate-resisting cement used only in concrete exposed to severe sulfate action – principally where soils or groundwaters have a high sulfate content. Table 1 describes sulfate concentrations requiring the use of Type V portland cement. Low Tricalcium Aluminate (C3A) content, generally 5% or less, is required when high sulfate resistance is needed
CEMENT TYPE, SUFFIX A
AIR-ENTRAINING AGENT INTERGROUND
Specifications for three types of air-entraining portland cement (Types IA, IIA, and IIIA) are given in ASTM C 150. They correspond in composition to ASTM Types I, II, and III, respectively, except that small quantities of air-entraining materials are interground with the clinker during manufacture to produce minute, well- distributed, and completely separated air bubbles.
These cements produce concrete with improved resistance to freeze-thaw action.
WATER CEMENT RATIO
COMPRESSIVE STRENGTH OF CONCRETE IS INVERSELY PROPORTIONAL TO PROPORTION OF WATER TO CEMENT USUALLY BETWEEN 0.45 - 0.60
concrete ratio definition
Define ratio of cement : sand : gravel by weight
such as 1:2:4 + amount of water
1 sack of cement weight? how much water?
4 to 4.5 gallons of water per 94 lb sack of cement
Rebar overlap
Rebar overlap is 30x rebar diameter
Bottom bars resist bending at midspan, stirrups resist diagonal forces at either end of the beam
Laitance
- chalky surface deposit, can develop when too much Water in the mix
concrete - Coating type sealers
Coating types - dry at the surface
- acrylics, urethans, epoxies
concrete - Penetrating type sealers
Penetrating types - seep into pores (do not wear off) -
silicones, silanes, siloxanes
Pre-stressing concrete
Pre-stressing is accomplished in one of 2 ways
Pre tensioning - in precasting plant high-strength pre-tensioning stranded cable or wire is draped in forms according to required stress patterned tensile force is applied, concrete poured and cured around it. once dry, cables are cut, and resulting compressive force is transferred to concrete
Post-tensioning - hollow sleeves or conduits are poured in. High strength steel tendons are stressed with hydraulic jacks after curing
concrete finish: Darbying or Floating
• Darbying or Floating is the finishing method that follows screeding and done by a hand float to smooth the surface further.
concrete finish: Screeding
concrete finishing method that is generally done with a 2 x 4 wood member to level the concrete surface after it is freshly poured?
concrete finish: Troweling:
• Troweling: If additional finishing is required for a more smooth interior applicaion, trowelling is the method to achieve it.
concrete finish: Machine Troweling
to achieve a non-slippery surface however since this is an indoor application, a smoother finish would be desired
concrete finish: burlap drag
Commonly used for outdoor applications, such as concrete pavement finishes by dragging a piece of burlap cloth on the surface of new poured concrete.
concrete finish: Coarse -bristled broom finishing:
Commonly used for outdoor applications with coarse or steel bristle. It is more slip resistant than trowel finish however if it is not done right, water can accumulate on it.
concrete finish: Sawing:
Also commonly used for out door applications to solve slip problems after concrete is done. Visit here for visual reference of each application.
advantages of air-entrained concrete
air-entraining agents have significant contributions to concrete, which includes:
Improved workability
Lower water–cement ratios
Improved durability and water tightness of the concrete
Advantages in cold climates where regular freeze/thaw is expected
Less risk of bleeding and a more uniform shape after formwork removed
Air-entraining agents has a little impact on cost and they don’t effect heat-resistance of the concrete.
