|
Hydraulic lime (HL) is a general term for varieties of lime (calcium oxide), or slaked lime (calcium hydroxide), used to make lime mortar which set through hydration: thus they are called ''hydraulic''. The other common types of lime mortar set through carbonation (re-absorbing carbon dioxide (CO2) from the air) and are sometimes called ''air lime''. Hydraulic lime provides a faster initial set and higher compressive strength than air lime and ''eminently hydraulic lime'' will set in more extreme conditions including under water. Calcium reacts in the lime kiln with the clay minerals to produce silicates that enable some of the lime to set through hydration; any unreacted calcium is slaked to calcium hydroxide which sets through carbonation: These are sometimes called ''semi-hydraulic lime'' and include feebly and moderately hydraulic lime, NHL 2 and NHL 3.5. The terms ''hydraulic lime'' and ''hydrated lime'' are quite similar and may be confused but are not necessarily the same material: hydrated lime is ''any'' lime which has been slaked whether it sets through hydration, carbonation, or both. The two basic types of hydraulic limes are ''natural hydraulic lime'' (NHL) and ''artificial hydraulic lime'' (AHL): Natural hydraulic lime (NHL) is produced by heating (calcining) limestone that ''naturally'' contains clay and other impurities: no materials may be added to create the hydraulicity. In the United States NHL may be called ''hydrated hydraulic lime'' (HHL) per ASTM C-141 Standard Specification for Hydrated Hydraulic Lime for Structural Purposes.〔(Michel Couvreux, "Selecting A Natural Hydraulic Lime: What To Look For" ''The Last Straw'' No. 62, Spring 2014. 8-10. Print. )〕 Artificial hydraulic lime (AHL) or artificial lime (AL) becomes hydraulic when hydraulic and/or pozzolan materials are added either before or after burning in a lime kiln. Artificial limes are more specifically identified as ''hydraulic lime'' (HL), as defined European Norm 459 (EN-459), "Consists of lime and other materials such as Portland cement, blast furnace slag, fly ash, limestone filler and other suitable materials.";〔 ''formulated lime'' (FL) (EN-459) consists of "...mainly of hydrated lime and or NHL with added hydraulic and/or pozzolanic material. It is identical to HL but its composition must be declared on the CE marking.";〔 ''pozzolanic hydraulic lime'' (PHL) (ASTM C-1707)is "very similar to HL or FL. Consists mainly of hydrated lime with one or more pozzolans with possible inclusion of inert filler. When Portland cement, even traces, is present (can be up to 20% of binder weight), it has to be labeled as 'PHLc'."〔 == Use in construction == Hydraulic lime is a useful building material for the following reasons: * It has a low elastic modulus. * There is no need for expansion (movement) joints. * It allows buildings to "breathe", and does not trap moisture in the walls. * It has a lower firing temperature than Portland cement, and is thus less polluting. * Stone and brickwork bonded with lime is easier to re-use. * Lime acts sacrificially in that it is weaker and breaks down more readily than the masonry, thus saving weaker stone such as sandstone and limestone from the harmful effects of temperature expansion and mortar freeze. * It is less dense than cement, thus less cold bridging. * Lime re-absorbs the carbon dioxide (CO2) emitted by its calcination (firing), thus partially offsetting the large amount emitted during its manufacture. The more hydraulic a lime, the less CO2 is reabsorbed during set, for example, 50% of CO2 is reabsorbed by NHL 3.5 during the set, compared to 100% of CO2 being reabsorbed by pure calcium hydroxide (fat lime putty). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「hydraulic lime」の詳細全文を読む スポンサード リンク
|