Week 3; uses of building materials
\nUnit 10 Construction Materials \u2014 Types and Uses
\n131
\nsand, coarse and fine aggregates, admixtures,
\nand water. When first mixed, it is
\nplastic
\n(able to
\nflow and be shaped) and can be cast to take the
\nshape of the formwork provided.
\nHardening of the concrete is caused by a
\nchemical reaction between the cement and water
\ncalled
\nhydration.
\nMost mixtures of concrete set
\nwithin 4\u201312 hours, depending on the tempera-
\nture, the volume of the pour, type of cement, and
\nadmixtures. When the temperature is below 70\u00b0F
\n(20\u00b0C), the reaction slows. Very little chemical
\nreaction takes place below 40\u00b0F (4\u00b0C), and
\nalmost none occurs at 32\u00b0F (0\u00b0C). The rule of
\nthumb is: if you are comfortable, the concrete is
\ncomfortable. Concrete continues to harden for
\nmonths after the initial set, but most placements
\nreach their compressive or design strength within
\n28 days. Forms can be removed after one to
\nseveral days or when the concrete can support
\nitself. This should be determined by an engineer.
\nTypes of Cement
\nCement
\nbinds the concrete mix together.
\nThere are a number of types of cement. The
\nmost common, used for general construction, is
\ncalled
\nType I Normal Portland cement.
\nAnother
\nvariation used in construction is
\nwhite Portland
\ncement.
\nIt is light-colored and used chiefly for
\narchitectural effects. White Portland cement is
\nmade from carefully selected raw materials and
\ndevelops the same strength as the normal gray-
\ncolored Portland cement.
\nTypes of cement include:
\n\u2022
\nType I, Normal Cement (most common)
\n\u2022
\nType II, Moderate Sulfate Resistance
\n(slow-reacting)
\n\u2022
\nType III, High Early Strength (fast-setting)
\n\u2022
\nType IV, Low Heat of Hydration (low heat
\ngeneration)
\n\u2022
\nType V, High Sulfate Resistance
\nThese other types of cements, along with
\naggregates and admixtures, are available to
\nproduce special types of concrete. Type IV is low
\nheat generation for large construction building
\nfoundation projects, such as dams. Others have
\nhigh early strength to produce concrete that sets
\nfaster than normal, permitting earlier form removal
\nand thus speeding construction. Still others are
\nmore resistant to deterioration caused by sulfates
\nand alkalis in the soil.
\nD
\nB
\nGravel
\nHead wall
\nA
\nRip-
\nrap
\nC
\nSand
\nPea gravel
\nFigure 10-2.
\nSamples of drawing symbols for gravel. A\u2014Plan view
\nof a headwall with rip-rap used to prevent erosion from
\ndrainage water outflow. This type of structure would be
\nfound on a site plan. B\u2014Plan view of a gravel
\ndriveway. C\u2014Section view of sand layer above pea
\ngravel. D\u2014Section view of crushed gravel.
\n132
\nSection 3 Specifications and Materials
\nConcrete Mixes
\nA concrete mix should be designed to
\nproduce the desired result. Characteristics and
\nproperties of concrete depend on the materials,
\nand their proportions, that make up the mixture.
\nThis will determine the workability, strength, dura-
\nbility, economy, volume stability, and appearance
\nof the finished hardened concrete. Enough water
\nis added to make the mix plastic, so that it will
\nflow into the forms. Too much water, however, will
\nreduce the strength and durability of the
\nconcrete, so the contractor needs to be careful. A
\ntypical mix would consist of 10% cement, 15%
\nwater, 25% fine aggregates, 45% coarse aggre-
\ngates, and 1% to 5% entrained or entrapped air.
\nAny material added to the concrete mix \u2014
\nother than cement, sand, aggregate, and water
\n\u2014 is known as an
\nadmixture.
\nAdmixtures are
\nused to make the mix more workable, retard or
\nspeed up hardening, increase freeze resistance,
\nor increase chemical resistance. Common admix-
\ntures to concrete include
\nair-entrainment,
\nused to
\nimprove durability in freeze\/thaw environments;
\nretarders,
\nused to slow down the initial set of
\nfresh concrete, especially in hot weather;
\naccel-
\nerators,
\nused to speed up the initial set of fresh
\nconcrete in cold weather;
\nwater reducers
\n, used to
\nreduce the amount of water required for a desired
\nworkability and water-to-cement ratio for strength,
\nand
\ncoloring agents
\n, used for altering the color of
\nthe concrete mixture. Concrete is typically trans-
\nported to the jobsite in a ready-mix truck.
\nReinforced Concrete
\nConcrete has great compressive strength, but
\nvery little tensile (pulling) strength. To overcome this
\nweakness, concrete is cast around steel
\nrein-
\nforcing bars
\n. These bars (commonly referred to as
\n“rebar”) have high tensile strength. As the concrete
\nhardens, it grips the steel to form a bond. The size
\nof the bar is indicated by the bar number, which is
\na multiple of 1\/8
\n\u2032\u2032
\n. For example, a #4 bar is 1\/2
\n\u2032\u2032
\nin
\ndiameter (4
\n\u00d7
\n1\/8
\n\u2032\u2032
\n= 1\/2
\n\u2032\u2032
\n). See
\nFigure 10-3.
\nRefer
\nto Unit 12 for more information.
\nReinforcing bars are round in shape, with
\nprojections (called
\ndeformations
\n) formed in the
\nrolling process to strength bonding with the
\nconcrete. Bars are placed after the forms are
\nconstructed,
\nFigure 10-4.
\nThe concrete is then
\ncast around the bars.
\nFigure 10-3.
\nReinforcing steel bars (“rebar”). Bar diameters are identified by a number that is a multiple of 1\/8
\n\u2032\u2032
\n. From left, bars
\nshown are #18, #14, #11, #9, #8, #7, #6, #5, #4, #3. The #18 bar is 2 1\/4
\n\u2032\u2032
\nin diameter; the #3 bar is 3\/8
\nDivision 06 \u2013 Wood
\nand Plastics
\nWood continues to be one of the chief
\nbuilding materials,
\nFigure 10-20
\n. It is used for
\nstructural framing (rough carpentry), trim, floors,
\nwalls, and cabinetry (finish carpentry and archi-
\ntectural woodwork). Relative to its weight, wood
\nhas high strength in compression, tension, and
\nbending. It also has excellent impact resistance.
\nWhile steps have been taken to substitute other
\nmaterials, wood remains a valuable and widely-
\nused residential construction material.
\nFigure 10-18.
\nThis steel frame is designed to support the entire
\nweight of the building.
\nFigure 10-19.
\nOpen-web steel joists combine strength with light
\nweight.
\nWood Classification
\nWoods are broadly classified as either hard-
\nwoods or softwoods. There are many varieties
\nused for construction. These classifications are
\nnot an exact measure of hardness or softness
\n(because this varies) but a general classifica-
\ntion based on type of tree. In addition to hard-
\nness or softness, woods vary in strength,
\nweight, texture, workability, and cost. Building
\nspecifications usually indicate the type and
\ngrade of lumber to be used in different parts of
\nthe construction.
\nAssignment<\/p>\n
Week 3; uses of building materials Unit 10 Construction Materials \u2014 Types and Uses 131…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,61],"tags":[],"class_list":["post-297","post","type-post","status-publish","format-standard","hentry","category-posts","category-second-term-jss1-basic-technology"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts\/297","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/comments?post=297"}],"version-history":[{"count":1,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts\/297\/revisions"}],"predecessor-version":[{"id":298,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/posts\/297\/revisions\/298"}],"wp:attachment":[{"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/media?parent=297"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/categories?post=297"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ecolebooks.com\/nigeria\/wp-json\/wp\/v2\/tags?post=297"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}