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Case Studies - Hydrated Lime

Hiway Stabilizers and Graymont

Product Sector: Industrial-Roading and Construction

Location: Silverdale, Auckland

Products: Burnt Lime and Hydrated Lime

Source/ Interviewee - Hiway Stabilizers

  • Graeme Quick fall, Business Development Manager
  • Mike Nelson, Operations Manager
     

Introducing Hiway Stabilizers

  • Hiway Stabilizers are New Zealand’s leading stabilisation specialists – with a company philosophy of sustainable civil engineering.
  • The stabilisation process involves modifying and strengthening existing clay materials for use in roading and construction projects – rather than using new materials to form a project base.
  • By avoiding costly and wasteful dumping of existing base materials, stabilisation offers significant economic, engineering and environmental benefits.

The challenge: getting lime in the right quantities, at the right time

  • According to Hiway’s Operations Manager, Mike Nelson, being able to respond quickly to project demands – where and when needed – is all in a day’s work.
  • “As a contractor, we need to be ready to go when the client wants and the weather demands. Also our volumes can be all over the place – because what we need varies depending on the weather, and the client’s general programme. The key thing we need from our lime supplier is the right volume, in the right location.”


Why Graymont?

Continuity of supply and delivery

  • Hiway uses a range of lime products. Calcium oxide (from 3mm minus to large clean chip) and hydrated lime is used in conjunction with specialised equipment, including computer controlled stabilising machines and piling rigs.
  • Having a ready supply of product, available in any volume, is critical to Hiway.
  • “McDonald’s (now Graymont) are by far the most significant lime supplier and can supply large quantities of product at short notice,” says Mike. “And their cartage contractors are excellent – they’re very reliable and provide exceptional service.”

Collaborative relationship

“We have a very collaborative relationship with McDonald’s (now Graymont),” says Mike Nelson. “We need them to be hugely flexible, and they are. They’re willing to increase storage and delivery capacity to meet demand – and that’s even meant providing additional onsite storage for some of the bigger jobs we’ve had to complete within tight timeframes in the past.”

Long association

  • Hiway Stabilizers was one of the first companies to pioneer the stabilising process in New Zealand more than 25 years ago, and McDonald’s Lime (now Graymont) has been their partner from the start.
  • “We’ve been dealing with McDonald’s Lime (now Graymont) since the early 1980s,” says Mike Nelson. “Quite simply, they deliver exactly what we need, when we need it.”

NZ Steel

Case Study: Lime and Steel Production

Product Sector: Industrial-Steel Production

Location: Glenbrook Steel Mill, New Zealand

Products: Burnt Lime, Limestone Chip and Hydrated Lime

Source/ Interviewee: New Zealand Steel-Connal Holmes, Principal Technologist, Steelmaking

 

Introducing New Zealand Steel

  • New Zealand Steel Limited is NZ’s sole producer of flat rolled steel products for the construction, manufacturing and agricultural industries
  • Using locally-sourced iron sand, NZ Steel produces around 620,000 tonnes of steel each year
  • The company is committed to being a world-class steelmaker, and exports about 60% of its steel output

The challenge: Securing top grade lime products to produce top grade steel

  • New Zealand Steel operates a fully-integrated steel mill at Glenbrook, about 60 kilometres south of Auckland
  • Crushed burnt lime transferred by pneumatic line of the steelmaking furnace, to generate slag to remove impurities from the steel
  • According to NZ Steel’s Principal Technologist, Steelmaking, Connal Holmes: “We need a very high grade limestone to produce the burnt lime – we can not have excessive levels of impurities like silica, which would cause wear on our transfer system.” The other specific requirement is the size of the lime; it cannot be larger than 1mm or it will not fluidise and inject via the tuyere [or nozzle] to the furnace interior. “We also use lump burnt lime at the ladle treatment station to create the slag that we want. We add limestone chip to the furnace as a coolant, and we use hydrated lime as a water treatment for pH control.”

Why Graymont?

  • Product quality/quality control

Graymont carries out routine chemical analysis and sizing checks to ensure that finely ground calcium oxide is supplied within tight standards that is required by New Zealand Steel.

  • A great relationship

“We have good communication and a very open way of talking with McDonald’s (now Graymont) . We have regular meetings, plant familiarisation visits to each other's operations and very few issues" says Connal. 

  • Long association

The two businesses share a long history.When McDonald’s relocated to the Waikato in the 1960s, it coincided with the opening of the Glenbrook mill.
“We’ve worked with McDonald’s ever since both our businesses began in the 1960s,” says Connal. “It’s a mutually beneficial relationship.”

Lime for Unit Masonry and Plastering

Product Sector: Industrial-Civil Contracting

Products Used: Hydrated Lime

Source: National Lime Association (4000 Brandywine Street, N.W., Washington, D.C. 20016)

 

Superior Masonry Construction

Specify Lime Mortar

Construction of sound masonry walls that are durable, weather resistant and require low maintenance depend on the following factors:

  1. Good architectural design, including relief joints where applicable.
  2. Highest quality mortar which has good workability, high water retention, strong bond, proven durability and weather resistance.
  3. Sound masonry units with low volume change and moderate rate of water absorption (suction).
  4. Proper workmanship, including the complete filling and tooling of all joints.
     

Lime is essential for high quality mortar

  • The essential ingredient for a good, all-purpose mortar is LIME…whether it is job-mixed with Portland cement, prepared masonry cement or is central-mixed (ready mixed mortar).
  • Be sure that the mortar contains LIME (calcium or calcium-magnesium hydroxide) and not inexpensive inert fillers like pulverized limestone (calcium carbonate).
  • Also, be sure that it contains enough lime to provide a workable, durable mortar that will provide watertight, sound masonry-at low cost.

Lime is time tested

  • Lime has been used universally for masonry since virtually the beginning of time. In fact, clay brick, stone and lime are the oldest building materials.
  • Attesting to lime’s durability are such famous structures as the Egyptian Pyramids, Parthenon, Great Wall of China and Roman Coliseum. All were constructed with lime mortar as the cementing or bonding agent.

 

Lime makes the ideal mortar

Workability

  • Lime makes mortar highly plastic and workable, enabling the mason to fill the joints completely without undue effort, resulting in better quality workmanship.
  • Mortar that is high in lime spreads easily under the trowel, increasing productivity.

 Water Retentivity

  • Plastic, workable lime mortars have high water retentivity, which means that such a mortar retains its water and resists suction or absorption by the masonry units.
  • A mortar with low water retentivity loses its moisture rapidly through absorption and “pancakes” or stiffens so quickly that intimate contact is not made with the unit.
  • Generally, as the lime content of mortars is increased, the water retentivity increases correspondingly. High water retention also minimizes the need for re-tempering the mortar.

Bond Strength

  • A mortar that fills joints completely will obviously produce more intimate contact with the masonry unit. As a result, it develops a better and stronger bond.
  • This kind of mortar also tends to ‘squish’ into the interstices and irregularities of the masonry unit, providing a “key ring” action which strengthens the bond.
  • Lime sticks to and works into the rough masonry surfaces, producing a tight mortar bond, which is the greatest possible prevention against leaky masonry.
  • However, bond strength has no relation to the crushing or tensile strength of mortar.

Ideal Strength

  • The right mortar should possess adequate compressive and tensile strength with a substantial safety factor.
  • Limit to the amount of strength desirable is 750-1000 p.s.i. (compressive strength) in 28 days. Thus, the strength of a mortar can be an illusory criterion of its quality.
  • Mortars should set with reasonable speed to enable construction to proceed with minimum delay.
  • The addition of Portland cement to a lime-based mortar provides the necessary acceleration of strength.

Elasticity and Flexibility

  • A mortar of modest but adequate strength (500-1000 p.s.i. range) has far greater elasticity than brittle mortars that are stronger and harder.
  • High lime mortar resists deflection (wind-sway) and lateral pressures better with less cracking in bond between mortar and units.
  • Thus, a strong intimate bond characterized by high lime mortars tends to “give a little” under stress.

Volume Change

  • There is less volume change (shrinkage) with mortars of lower but adequate strength.
  • Hard, high-strength mortars tend to shrink after hardening, producing separation  cracking between the mortar and units, resulting in a loss of bond. Of all cementitious materials, lime possesses the least volume change.

Autogenous Healing

  • The ability of a mortar to reknit itself if voids are present or if small cracks develop between the mortar and the masonry unit is called autogenously healing.
  • High lime mortars have this characteristic. Nature provides this cure by rain water and atmospheric carbon dioxide.
  • Gradually, this chemical reaction (similar to the formation of stalactites) plugs the crack or interstice.

Efflorescence

  • The two prime causes of efflorescence are the improper protection of masonry units in walls under construction from rain or snow, and the presence of soluble salts (chlorides and sulphates) in the masonry materials.
  • To protect the masonry units use a high lime mortar to provide tight joints and prevent the entrance of water.
  • Thus, the water cannot act as a catalyst and dissolve the salts which later dry and and crystallize as the unsightly “building bloom.” Its is a chemical fact that lime contains less soluble salts than any other masonry material.
  • However, regardless of the mortar used, masonry units and walls under construction should be covered with tarpaulins to prevent absorption of rain water.

Weather Resistance

  • A mortar should be durable and able to resist high winds, freezing, thawing, wetting and drying cycles.
  • Lime based mortars increase in strength steadily over a period of many years.
  • Actually, wetting and drying cycles are beneficial to such mortars and tend to accelerate this gain in strength.
  • Under freezing conditions the tight mortared joints prevent entrance of water and the disruptive effect of subsequent ice crystals in the wall.

Economy

  • A mortar should be economical to use.
  • In addition to being relatively inexpensive, lime has the greatest sand carrying capacity of any cementitious material.
  • This means by virtue of its high plasticity, lime can accommodate a high percent of sand and still be workable-as much as 1:4½. In addition, there is less mortar wasted by droppings because of its tendency to stick to the units.
  • Its slow setting characteristic also offers economy by minimizing re-tempering.
  • Due to high workability, there is low labour cost in mixing and brick laying.
  • Finally, high lime mortars are durable and require a minimum amount of maintenance.  

Lime for Stucco

  • For beauty and versatility, exterior plaster (stucco) buildings have been unsurpassed through the centuries.
  • Now architects can blend improved stucco with modern design to provide colourful and functional buildings.
  • If proper blending of materials is employed and if they are properly applied, plaster will provide a low-cost permanent method of facing homes and buildings.
  • It is also widely used as a low-cost effective method of modernizing old residences.
  • As in the case of masonry mortar, a good lime-cement plaster should contain an adequate amount of lime in order to provide elasticity, reduce shrinkage and cracking, improve workability-yet give sufficient strength.
  • Since plaster is non-load bearing, it is unnecessary to use high strength, quick setting mixes. In fact, more elastic stuccos containing adequate lime have excellent bonding characteristics.
  • More over, unlike cement plaster, high lime stuccos offer architects the opportunity to develop bright colourful designs. Or, if desired lime’s whiteness can be an asset to either interior or exterior construction, aesthetically.

Stabilising soils and expediting construction at building sites

  • Hydrated lime is increasingly used in soil stabilization for the construction of a stabilized subgrade, sub base, or base course for all types of roads, parking lots, loading areas, temporary haul roads, and to ”beef up” the subgrade under concrete slab building foundations.
  • Lime reacts with clay-bearing soils and gravels, stabilizing them against shrinkage and swell and hardening these soils by a complex cementing reaction.
  • Thus, the addition of lime permits the use of sub marginal granular materials and unstable clays and silts and obviates the need of undercutting and wasting these materials for replacement by often expensive, hauled-in base course and select borrow materials.