AU2001272205A1

AU2001272205A1 - Mortar composition and method

Info

Publication number: AU2001272205A1
Application number: AU2001272205A
Authority: AU
Inventors: Liam P. Devlin; Edita Grujic; Samuel Moses
Original assignee: Parexgroup Pty Ltd
Current assignee: Parexgroup Pty Ltd
Priority date: 2000-07-14
Filing date: 2001-07-13
Publication date: 2002-05-02
Anticipated expiration: 2021-07-13

Description

MORTAR COMPOSITION AND METHOD

Field of the Invention

The present invention relates to an improved mortar composition. In particular, the invention relates to a mortar composition containing untreated rice husks and which composition can exhibit higher mileage and lower density than standard mortar compositions. The present invention also relates to a method for the preparation of said mortar composition.

Background of the Invention

Hydraulic cements have been used for thousand of years as the agents in adhesives, cement pastes, mortars, grouts, cement panels and bricks, and concrete. The hydraulic cement- based materials are formed by mixing hydraulic cement with water and one or more fillers, which are either simultaneously or subsequently blended into the mixture. When water is added to hydraulic cement, the existing minerals in the cement either decompose or combine with water, and a new phase (such as a calcium-silicate-hydrate structure) forms throughout the material. The water-cement mixture containing the fillers sets and then cures. Wetted hydraulic cements are typically used as an adhesive between two substrates such as a concrete floor or wall and a ceramic tile, between bricks or cinder blocks, as a filler, sealant or stucco, as individual bricks or cement panels, or with the addition of aggregates as concrete blocks, footpaths, roads, columns, walls, floors, supports or other such structures.

The use of cellulosic material as a filler or extender for hydraulic cement compositions has been previously described. The use of fillers or extenders gives rise to new cement compositions having unique and advantageous qualities, in addition to extending the coverage of the cement composition, and, where the filler has a low density, in making light-weight cement based compositions and products. However the use of such cellulosic material often retards cementitious compositions resulting in products having lower strength, poorer keeping qualities by being susceptible to rotting and degradation, and lower impact resistance. Portland cement bonded lignocellulosic materials are known to have a detrimental effect on the strength and quality of cement compositions. Typical lignocellulosic materials which cause retardation include various wood particles such as rice husks, jute sticks, coir, sawdust, coconut pith, banana stem fibre and wheat straw. It is thought that in the setting of cement-wood particle compositions that a weak boundary layer is formed between the calcium silicate hydrate and the wood particles as a result of the dissolution of polysaccharide and lignin released during the setting of the cement by calcium hydroxide. The addition of wood particles to cement compositions gives rise to weak and inferior products as a result of the poor adhesive forces operating between wood particles and the hydrated products of cement [see Singh, S.M., J Indian Acad. Wood Sci., 10(l) pl5-19 (1979)].

Problems associated with retardation by rice husks and other cellulosic particulate material in hydraulic cement compositions has been either tolerated (Singh, S.M., referenced above), or addressed by chemically modifying the rice husks. For example, Japanese patent application No. 60-245679 describes dried rice hulls being impregnated with a urea solution. The processed hulls are dried at 100-250°C and crushed into a fine 150-300 mesh powder. The processed rice hull powder is used as an extender for tile adhesives.

Japanese patent application No. 55-144072 describes heat-treated vegetable fibrous material used as a filler for adhesives. The vegetable fibrous material such as wood powders, leaves, barks, spike axes of maize or rice hulls, is optionally ground, then heat- treated by contacting it with saturated steam or superheated steam at preferably an elevated pressure. The heat-treated material is dried to a moisture content of 3-15%, and is then blended with a filler with an adhesive based on a resin such as a urea resin, a melamine resin or a phenol resin.

Chinese patent application No. 1060428 describes the preparation of thermal-insulating board with treated rice husks. The rice husks are antiseptically treated by immersion and boiling, followed by binding together with an adhesive and pressing to form a husk board, and finishing with a water-proof cement sealing coat to obtain thermal-insulating board.

Numerous other prior art references describe the use of ashed rice husks in cement and concrete products. The rice hulls or husks are roasted or burnt then mixed with lime or other cementitious compounds to prepare bricks, clinkers and various other cement products.

The advantages gained by using treated rice husks as extenders are often out-weighed by the disadvantage of having to chemically treat or modify the rice husks before they can be effectively used in cement products, mortars, bricks, concretes and the like. The time and processing steps required for making rice husks and other cellulosic material suitable for use as extenders in mortar and cement products is often inconvenient and financially prohibitive.

A requirement accordingly exists for a mortar composition which exhibits higher mileage and lower density by the simple addition of untreated cellulosic particles, but where the adhesive shear and tensile strength of the cement-cellulosic particle based mortar composition is not substantially compromised. Thus it is a preferred object of the present invention to overcome or at least ameliorate problems associated with the strength and binding of cement-cellulosic particle based mortar compositions, or at least to provide an alternative mortar composition for use in the building industry. Further advantageous outcomes achievable by embodiments of the present invention include the provision, of mortar compositions at a reduced cost and which are lighter but as strong and durable as known mortar compositions commonly used in the building industry.

Summary of the Invention

The present inventors have surprisingly found that particulate cellulosic material such as untreated rice husks can be used to extend hydraulic cement compositions, whilst the compositions still exhibit acceptable tensile and shear strengths. The hydraulic cement compositions of the present invention comprise cement, rice husks, at least one or more fillers and additives and an accelerator.

Thus according to an aspect of the present invention there is provided a mortar composition which comprises: a) 100 parts by weight of cement; b) 1-80 parts by weight of untreated rice husks; c) 30-200 parts by weight of at least one or more fillers and additives; and d) 0.2-10 parts by weight of an accelerator.

According to another aspect of the present invention there is provided a method of making a mortar composition comprising the step of mixing together in any order: a) 100 parts by weight of cement; b) 1-80 parts by weight of untreated rice husks; c) 30-200 parts by weight of at least one or more fillers and additives; and d) 0.2-10 parts by weight of an accelerator.

The present invention also provides mortar compositions prepared by the above method.

According to still another aspect of the present invention there is provided a settable mortar composition which comprises: a) 100 parts by weight of cement; b) 1 -80 parts by weight of untreated rice husks; c) 30-200 parts by weight of at least one or more fillers and additives; d) 0.2-10 parts by weight of an accelerator; and e) 30-150 parts by weight of water.

According to yet another aspect of the present invention there is provided a method of making a settable mortar composition comprising the step of mixing together in any order: a) 100 parts by weight of cement; b) 1-80 parts by weight of untreated rice husks; c) 30-200 parts by weight of at least one or more fillers and additives; d) 0.2-10 parts by weight of an accelerator; and e) 30-150 parts by weight of water.

According to another aspect of the present invention there is provided a method for setting a tile on a supporting surface which method comprises trowelling onto the supporting surface a settable mortar composition of the present invention and setting the tile into the mortar composition to adhere the tile to the supporting surface.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

Detailed Description of the Invention

As used herein the term "cement" refers to binder materials that harden to form a connecting material between solids and typically include any mixture of finely-ground lime, alumina, and silica that will set to a hard product and which combine with other ingredients to form a hydrate such as Portland cement, hydraulic cements, blended cement and masonry cement, mortar, grout, and may also have added fillers, aggregates and/or other additives including hydrated lime, limestone, chalk, shell, talc, slag or clay.

As used herein the term "mortar" is taken in its broadest sense to mean a hydraulic cement composition such as a masonry cement, grout, tile adhesive, filler, screed, stucco or plaster especially suited to bind bricks, stones, tiles, blocks and the like either together or to other substrates.

Ordinary Portland cement is a hydraulic cement produced by pulverising Portland cement clinker and typically is classified as one of 8 Types: I; II; III; IN; V; la; Ila; and Ilia. Variations in the colour of the cement may exist such as white Portland cement or grey Portland cement, or the cement may also be pigmented or coloured if required.

The present inventors have surprisingly found that hydraulic cement compositions can be prepared with cellulosic material such as wood-based particles which compositions maintain an acceptable level of tensile, bond and shear strength, durability, flexibility, resilience and resistance to cracking and breaking of the bond or the substrate whilst gaining substantial advantages in extending the mileage of cement compositions. In a particularly preferred embodiment the coverage of cement compositions when used as mortars and tile adhesives is significantly increased by the addition of cellulosic material without significantly compromising strength, and in some cases maintaining the strength of the hardened cement. Furthermore the cement compositions of the present invention also have lower densities than those without the added cellulosic material.

In a particularly preferred embodiment of the invention, the wood-based cellulosic particulate material of the present invention is untreated rice husks. Rice husks are readily available as a byproduct of the rice-growing industry and have excellent utility in the cement compositions of the present invention. The rice husks (or hulls) are most preferably used untreated by any chemical processing step. The rice husks are obtained from the bran or outer sheath of the rice grain separated during normal milling of rice. The sheer volume of rice grown and milled around the world means that thousands of tonnes of waste rice husks are produced annually, providing an inexpensive and reliable source of the cellulosic extender for use in the mortar compositions of the present invention. In addition, the use of untreated rice husks in the mortar compositions addresses environmental concerns as to how to dispose of the waste rice husks.

Further and important advantages of using rice husks in the mortar compositions of the present invention are that the husks are used as is, untreated, without any chemical processing as typically required in prior art methods and compositions. Utilising the untreated husks lowers processing costs, minimises plant costs and obviates the need of disposing of chemical processing wastes from chemically treating the rice husks. The rice husks may be used as is or sized according to the application in which they will be applied. For example where the mortar composition is to be used as a screed, stucco, rendering composition or the like, the husks can be used as is. Alternatively it may be desirable to reduce the size of the husks by, for example, grinding with sand or other abrasive techniques well known in the art. Grinding the rice husks produces a range of smaller particle sizes which again may be used as is or sieved to give particular size ranges.

Reducing the size of the rice husk particles allows for the wetted mortar composition to flow more easily. If the rice husk particles are too large the ability for wetted compositions to be spread with a grooved trowel for example is diminished as the husks tend to clump and stick together in the grooves. The rice husks obtained from the milling of rice are simply dried, and if desired can be sieved to obtain a preferred particle size distribution. Rice husks may be ground or milled and then sieved to provide a more preferred size range and better distribution of rice husks as required.

The typical size distribution of the ground rice husks obtained from the Rice Growers Cooperative in Australia (COPRICE) and used in the compositions exemplified herein is as follows:

Husk Size Distribution

+ 425 μm 26%

+ 300 μm 31% + 150 μm 32% pan 11%

100%

The untreated rice husks for use in the present invention are preferably from 1-80 parts by weight (based on 100 parts by weight of cement), more preferably 20-40 parts by weight, and most preferably 30-35 parts by weight. When grooved trowels are used to spread the wetted mortar compositions, the untreated rice husks are preferably in the size range of 100-600 microns, more preferably 150-500 microns.

The untreated rice husks are added to mortar compositions of the invention, either in addition to the existing components or by replacing some of the filler to keep the cement ratio constant as required. The present inventors have found that the judicious choice of accelerator or setting aid can overcome the problem that particulate cellulosic material such as untreated rice husks do not bind well with wetted cement compositions and the cellulosic material retards the strength of the cement composition once set.

According to a preferred embodiment of the present invention the accelerators are selected from C _-4 carboxylic acid salts. Preferably the carboxylic acid salt is formate, acetate, propionate, oxalate or malonate more preferably formate or acetate, most preferably formate, whilst the counter ion is preferably calcium. It will also be understood that other counter anions such as magnesium, potassium, lithium, sodium, ammonium or the like can be used where there is a high calcium cation content in the mortar compositions of the invention provided by fillers, additives or other accelerators. The use of standard and common accelerators on their own such as lithium carbonate or calcium chloride gives no significant or real advantage in compensating for the retardant properties of the untreated rice husks.

Good results are also obtained with certain other accelerators and particular mention is made of nitrate salts, and most preferably calcium_nitrate as a suitable accelerator for the mortar compositions of the present invention.

Preferably the accelerator is in an amount of 0.2-10 parts by weight (based on 100 parts by weight of cement), more preferably 2-6 parts by weight, and most preferably about 4 parts by weight.

The accelerators of choice in the present invention work by restoring the strength lost by addition of the particulate cellulose material to the hydraulic cement compositions. In particular, and as shown by the Examples which follow, calcium formate and other accelerators are able to offset the retardation caused by the untreated rice husks in the mortar compositions of the invention.

A further advantage in using untreated rice husks is their ready availability in bulk on a multi-tonne scale. The rice husks are used untreated, eliminating the need to perform any chemical pre-treatment steps. As noted above, the husks may be physically treated, such as for example simple washing to remove unbound polysaccharides, drying or grinding and/or sieving to preferred particle size ranges or distributions.

The mortar compositions of the present invention preferably contain at least one inert filler. Fillers that may be used include aggregate filler, fine filler or a combination of aggregate and fine fillers. The inert filler additive may be silica sand, limestone, perlite, volcanic aggregate, alumina trihydrate, ground quartz, volcanic ash, fine sand, talc, mica, clays, calcium carbonate (marble dust), other clean inert material or mixtures of the foregoing.

In mortar compositions of the present invention the fillers are often fine fillers, typically with particle sizes in the range of 1 microns to many millimetres in diameter and may include the following materials: silica or alumina materials such as fine or ground sand, ground silica, colloidal or precipitated silica and corundum; carbonates such as natural or surface treated magnesium or calcium carbonate, or a calcium, barium or magnesium carbonate such a dolomite; sulfates such as calcium sulfate, for example, hydrated plaster and gypsum, insulation materials such as expanded glass or clays, vermiculite, perlite and celite; expanded plastics such as polystyrene and polyurethane; crumbed rubber; metal filings; shortmilled fibres, mica and other such materials.

Sand and other such fine aggregates used as fillers in the mortar compositions of the present invention typically have particle sizes in the range of substantially 0.1 mm to 6 mm and may include the following materials: common or silica sand, light weight aggregates such as perlite, vermiculite, fly ash, pumice, expanded clay, expanded polystyrene beads and carbon beads.

The mortar compositions of the present invention may be used as grout, mortar, backerboard, floor screed, stucco and as a tile adhesive in construction and building projects. Mortar, adhesive, grout, backerboard, screed and stucco are all cementitious products similar in composition but designed, applied and used for different but related objectives. Typically, grout is a thinner mortar used for the filling of spaces between tiles and masonry to provide a finish comparatively level with the surfaces of the tiles and masonry, for both aesthetics and ease of maintenance. When the grout solidifies it provides a monolithic structure to the multitude of tiles, bricks or other products that have been grouted. Grout is a bonding agent which must bond well into the spaces in which it is applied to.

Mortar or adhesive is a basic combination of a fine particulate filler such as fine sand and Portland cement. Typically the adhesive is used as a bonding agent for the laying of tiles, bricks and other masonry products onto a substrate such as a wall, floor or backerboard. Typically tile adhesives are used exclusively as a bonding agent to create the adherence of two separate substrates, such as tile to concrete.

Backerboard is a solid sheet of cementitious material which provides a sound and stable substrate for the installation of tiles and masonry materials, such as ceramic tiles or thin brick veneer. Backerboard is used as a substrate to which other products are bonded to, such as with mortars, adhesives and mastics.

In the setting of tiles, a proper substrate must first be in place to support the tiles that are then bonded to the substrate. Concrete floors may require some degree of levelling with, for example, cement pastes and fillers onto which the tiles are then applied. The mortar compositions of the invention also find utility as such cement pastes and fillers. Other substrates known to those skilled in the art such as backerboard or metal lath with cement plaster applied to it may find utility as an adequate substrate. With the substrate in place, the tiles are set into a wetted mortar or adhesive composition. Typically the mortar or adhesive is generally trowelled onto the surface of the substrate using a ridged trowel which provides for ridges of typically about 12 mm in height and spacing. However the height and spacing of the grooves, if any, may vary according to the fluid nature of the mortar, the size and type of tile being laid and to the particle size distribution of the rice husks in the mortar compositions as will be apparent to those skilled in the art. When the tile is set into this mortar bed, any ridges present permit the air to escape from under the tile and also provides areas into which the mortar may spread when the tile is set.

The hydraulic cement compositions of the invention may also be used in the production of pre-mix concrete. As used herein the term "concrete" is broadly defined as a hard, strong building material made by mixing a water-hydraulic cement mixture with an aggregate such as sand, gravel, other geologic materials, metals and/or metallic alloys having a typical particle size in the range of 6 mm to 50 mm. The cement acts as a "glue" to bind the aggregate particles together in the concrete. The physical properties of concrete vary depending upon many variables including the cement composition, the choice of aggregates, and the processing technique. Concrete is commonly used to construct driveways,^*footpaths, foundations, floors, roads, walls, supports and other such structures.

It is known that the properties of mortar compositions can be substantially affected by varying the amount of water added to the cement composition mixture prior to setting and hardening. Typically, reducing the amount of water tends to improve the strength of the set and hardened product. However a certain minimum amount of water is needed in order to obtain the required workability or fluidity, and so water content may be reduced if special techniques are used such as: adding plasticisers to the fresh mix; selecting a proper grading of aggregates used in the mix; selecting greater amounts of high aluminous cements in place of Portland cements; using vibration to place the mix which means less workability is needed; removing water after the fresh mix is in place; and by adding latexes. The amount of water required to be mixed with the hydraulic cement compositions of the invention is preferably 30-150 parts by weight (based on 100 parts by weight of cement), more preferably 60-100 parts by weight. However, it will be understood that those skilled in the art may vary the amount of added water depending on various factors such as rate of setting required, amount of latex to be added, desired workability of the wet mixture and the like.

Those skilled in the art will also know that it may be desirable to pre-moisten the surface of the substrate to limit the amount of liquid absorbed from the settable mortar composition by the substrate, particularly where porous substrates are used. In addition to pre-moistening the surface of the substrate, it may be desirable to clean or pre-treat the surface in preparation for binding to the other substrates such as a tile. Such pre- moistening or cleaning can be accomplished through a variety of ways as known to those skilled in the art.

The mortar compositions of the present invention may also contain elastomeric or amorphous thermoplastic polymer particles as redispersable powders or dispersions. The main elastomeric latexes are natural rubber, styrene butadiene, polyacrylonitrile butadiene, polychloroprene. The primary thermoplastic latexes are: polyvinylacetate, polystyrene, polyvinylchloride, polyacrylates, or their copolymer. Latexes allow reduction of the amount of water used in the preparation of the settable cement compositions since the latexes have a plasticising effect on the mix. Latexes also form a 3 -dimensional film throughout the mortar or concrete on drying and this provides additional beneficial effects such as higher strength, -greater wear resistance, greater durability, greater flexibility and improved resistance to chemical attacks. Latex modified mortars and concretes typically also have a much higher bonding strength with other materials compared to unmodified cement based mortars and concretes.

Conventionally, latexes are added to mortar or concrete by adding a small amount of latex to the fresh mix and reducing the amount of water to the extent that the same workability is attained. Generally, when latex is added to conventional mortar or concrete mixes, the latex modified mortar or concrete can be obtained with a smaller water/cement ratio of up to about 35%. In addition, the latex additives are typically anionic and nonanionic dispersions in water, usually containing approximately 50% by weight of water, and this water must be considered as part of the mixing water.

The mortar compositions of the present invention optionally contain further additives which assist in controlling the curing rate, strength on setting and hardening and general properties of the compositions. These additives may include suspension enhancing agents which decrease the settling of components thereby aiding the stabilisation of the cement composition. Some of the preferred suspension enhancing agents as well known in the art include cellulose ethers, animal glues, starches, polyvinyl alcohols, proteins, gums, clays and any combination of the foregoing.

Setting aids are optionally employed in cement compositions to help promote faster, harder curing and/or to prevent efflorescence. The most common setting aids are salts that provide free calcium ions to the aqueous component and such salts typically include calcium chloride, calcium sulfate and calcium nitrate.

It may be desirable to add a dispersant or a surfactant to aid in the uniform distribution of cement compositions. Fatty amines, alkyl amines, ethylene oxide condensates or sulphonated soaps may be used as dispersants. The most preferred dispersants are anionic or nonionic surfactants as well known in the art. Additional dispersant aids such as sodium naphthalene formaldehyde sulfonates or sulphonated melamine formaldehydes may also be used. It may also be desirable to add preservatives, antifoaming agents or other miscellaneous enhancing additives such as alkylene glycols, chlorinated paraffins, and alkali metal fatty acid salts as known to those skilled in the art.

The fillers and additives used in the mortar compositions of the present invention are preferably one or more of calcium carbonate, hydroxy alkyl cellulose ethers, ethylene/vinyl acetate copolymers and terpolymers and the like, polyvinyl alcohol, hydrated lime, and fine sands present in a total amount of 30-200 parts by weight (based on 100 parts by weight of cement), preferably about 30-150 parts by weight and more preferably about 45- 120 parts by weight.

More preferably the fillers and additives based on 100 parts by weight of cement include: - calcium carbonate present in up to 25 parts by weight, more preferably about 3-16 parts by weight;

- hydroxy alkyl cellulose ethers in the range 0.1-3 parts by weight, more preferably about 0.2-1 parts by weight and preferably consists of water soluble thickeners and colloids such as but not limited to hydroxy propyl methyl cellulose, hydroxy ethyl cellulose, ethyl hydroxyethyl cellulose, acrylamide modified polymers, starches, polysaccharides, xanthan gums, other thickeners well known in the art and mixtures thereof;

- ethylene/vinyl acetate copolymers in the range 0.1-10 parts by weight, more preferably about 1-3 parts by weight; - polyvinyl alcohol in the range 0-10 parts by weight, more preferably about 0.7-4 parts by weight; hydrated lime in the range 0-6 parts by weight, more preferably about 2 parts by weight; and

- fine sand in the range 25-150 parts by weight, more preferably about 30-110 parts by weight, and typically having a nominal particle size range of about 150-500 microns.

Other optional ingredients may be present in amounts from about 0.01 to about 20 parts by weight (based on 100 parts by weight of cement) of a setting aid, an antifoaming agent, a glycol, a latex, a waterproofing agent, a preservative, antimicrobial agent, an additional setting aid or mixtures thereof.

The components of the mortar compositions may be added together in any preferred order and may be mixed typically by agitation, rolling or shaking. It will also be obvious that two or more components may be mixed together and at a later time further compounds added to make the mortar compositions of the invention. Any such variations in the order of mixing the compounds in the preparation of the mortar compositions are contemplated by the invention, including the pre-mixing of the untreated rice husks with the accelerator, in particular the carboxylic acid salt, with or without water or moisture, prior to the addition of the remainder of the components.

The hydraulic cement compositions of the invention show particular utility as mortars and tile adhesives. Mortar compositions of the invention are able to achieve excellent shear and bond strengths to industry standards, such as the Australian Standard AS 2358, and exhibit desired properties; whilst at the same time being able to be formulated at similar or lower costs per square metre covered than most presently known mortar compositions.

Whilst not wishing to be limited to theory, it is believed that the carboxylic acid salt accelerator, such as in particular calcium formate, may react in situ with the untreated rice husks by countering the polymeric and lignocellulosic material to increase the bond strength of the cement to the surface of the husks. The rice husks in the presence of the calcium carboxylic acid salt wets well and forms strong bonds to the cement. When looking at the fine structure of the untreated rice husks, the husks appear as thin fibrous matted sheets which, with the assistance of the calcium carboxylic acid salt accelerant, are able to bond strongly in the hardened cement composition. The high silica content of the rice husks is also thought to contribute to their ability to form strong bonds with the components of the mortar compositions once set, with the aid of the calcium carboxylic acid salt accelerator.

The invention is further described in and illustrated by the following Examples. The Examples are not to be considered as limiting the invention in any way. Example 1 Basic Mortar Compositions

Vinnapas LL SlOO - ethylene/vinylacetate copolymer Omyacarb 40 - calcium carbonate Walocel MKX 45000 - hydroxy ethyl cellulose PVA BP 20S - poly(vinyl alcohol) Clay Q38 - kaolin Agitan P823 - paraffin on inorganic carrier

The mortar compositions are prepared by adding the ingredients in any preferred order and mixing typically by agitation, rotation or shaking. Typically different size lots may require modification to the addition and mixing steps as well known to those skilled in the art.

All amounts are shown as parts by weight. The proportion of rice husks in mortar composition A is 18% by weight, whilst the proportion of rice husks is 15% in composition B and 12.5% in composition C. Example 2 Series Av. General parameter variation in mortar composition A

Vinnapas LL 5100 ethylene/vinylacetate copolymer Omyacarb 40 calcium carbonate Walocel MKX 45000 hydroxy ethyl cellulose Methocel 228,240S hydroxypropyl methyl cellulose PVA BP 20S polyvinyl alcohol

The mortar compositions were prepared by the general method described in Example 1. All amounts are shown as parts by weight.

Example 3 Series Bv. General parameter variation in mortar composition B

Vinnapas LL 5100 - ethylene/vinylacetate copolymer Omyacarb 40 - calcium carbonate Walocel MKX 45000 - hydroxy ethyl cellulose Methocel 228,240S - hydroxypropyl methyl cellulose PVA BP 20S - polyvinyl alcohol

Example 4A Series Aa. Accelerator variation in formula A

Vinnapas LL 5100 - ethylene/vinylacetate copolymer Omyacarb 40 - calcium carbonate Walocel MKX 45000 - hydroxy ethyl cellulose

Example 4B Blank Series BR. Series Aa without rice husks

Vinnapas LL 5100 ethylene/vinylacetate copolymer Omyacarb 40 calcium carbonate Walocel MKX 45000 hydroxy ethyl cellulose

Example 4C Blank Sand Series BS. Series Aa with rice husks replaced by sand

Example 5 Series Av, and Series Bv and C. Bond strength tests for cement compositions of Series Av, Series Bv and C

The mortar compositions of Series Av and Series Bv were mixed with water in a 2:1 ratio (compositiomwater) unless otherwise stated, whilst the mortar composition of Series C was mixed with water in a 2.9:1 ratio. The compositions were mixed by mechanical agitation until a soft paste formed. The wet mortar compositions were let stand for 10 minutes before being used to assemble two ceramic tiles with a 13 mm offset in accordance with Australian Standard 2358. Results shown indicate the shear bond strengths (MPa) for tiles allowed to dry for 7 days (7d), 14 days (14d) and dried for 7 days and immersed in water for 7 days (7/7d) in accordance with Australian standard AS 2358, sections 3.2-3.4.

The results depicted in Example 5 above clearly show the utility and advantages of the untreated rice husk/calcium formate accelerator mortar compositions of the present invention. The 7 day strengths, 14 day strengths and 7 day dry/7 day wet strengths are all very good to excellent across the range of rice husk-mortar compositions.

Example 6 Bond strength test for mortar compositions of Series Aa, Blank Series

BR (without rice husks) and Blank Sand Series BS (rice husks replaced by sand).

The mortar compositions of Series Aa and the Blank Series BR were mixed with water in a 2:1 ratio (composition: water) unless otherwise stated, whilst the compositions of the Blank Sand Series BS were mixed with water in a 3:1 ratio. Sets of ceramic tiles were assembled with the wet mortar compositions of Series Aa, BR and BS as described in Example 5. Results shown indicate the shear bond strengths (MPa) for tiles allowed to dry for 7 days (7d), 14 days (14d) and dried for 7 days and immersed in water for 7 days (7/7d) in accordance with Australian standard AS 2358, sections 3.2-3.4.

The results depicted in Example 6 above clearly show the utility and advantages of the untreated rice husk/accelerator mortar compositions of the present invention.

Blank sand series BSO is a typical sand/cement mortar composition which exhibits excellent tensile and sheer strength when tested to AS 2358. When a significant portion of the sand is replaced with untreated rice husks (series code AaO - i.e. no accelerator) the strength of the resultant mortar composition drops markedly to well below the accepted standard. Untreated rice husks clearly act as a retardant.

The blank series BR corresponds to the rice husk accelerator series Aa, but where the rice husks are not present and are not replaced by any other filler, such as sand. It can be seen from series BRO that omission of the retarding rice husks from series AaO allows for an increase in the strength of the mortar composition, approaching but not to the level of the full sand series BSO.

Adding commonly used accelerators to the rice husk series Aa provides little or no improvement in the strength of the mortar compositions. For example the addition of a high dose of lithium carbonate (0.4%) (series Aa2) shows minimal improvement over Series AaO. The addition of a moderate dose of calcium chloride (1.5%) (series Aa3) gives some improvement in strength but it is not until a high dose of calcium chloride is used (3.75%)) (series Aa4) that the strength approaches that of the Australian standard. However such high contents of calcium chloride is preferably avoided as problems of shrinkage and hence loss of strength over long periods of time sometimes occurs. Therefore the well- known cement accelerators are generally not very good at countering the retardation attributed to the untreated rice husks.

Excellent and surprising results are obtained however with carboxylic acid salts such as sodium formate (series Aa5 and Aa6), calcium formate (series AalO, A and Aal), ammonium formate (series Aa7) and calcium acetate (series Aa8). The strength imparted by calcium acetate is most surprising given that it is not considered an accelerator for cement. In fact in blank sand series BS8, the addition of calcium acetate causes retardation of the mortar strength at 14 days and 7/7 days when compared to the mortar composition without accelerator (series BSO). The fact that carboxylic acid salts are able to compensate for the retardation caused by the untreated rice husks is most unexpected.

Best results are shown by 4% calcium formate (series A) where the strength of the mortar compositions at 7 days and 14 days is comparable to that of blank sand series BS (where the rice husks are replaced by sand) and the blank series BR (where the rice husks are omitted but not replaced by sand).

Further surprising results are shown by calcium nitrate (series Aa9) in which rice husk mortar compositions show good strength.

Example 7 Series Ap. Powder polymer variation in Series Av8

Vinnapas and Elotex - cement compatible polymeric binders known to those skilled in the art Omyacarb 40 - calcium carbonate Walocel MKX 45000 - hydroxy ethyl cellulose Methocel 228,240S - hydroxypropyl methyl cellulose PVA BP 20S - polyvinyl alcohol The mortar compositions were prepared by the general method described in Example 1. All amounts are shown as parts by weight.

Example 8 Bond strength tests for mortar compositions Series Ap (power polymer variation) based on composition Av8

The mortar compositions of Series Ap were prepared with water in a 2:1 ratio (composition: water). Sets of ceramic tiles were assembled with the wet mortar compositions of Series Ap as described in Example 5. Results shown indicate the shear bond strengths (MPa) for tiles allowed to dry for 7 days (7d), 14 days (14d) and dried for 7 days and immersed in water for 7 days (7/7d) in accordance with Australian standard AS 2358, sections 3.2-3.4.

Example 8 shows variations in powder polymers wliich may be used in untreated rice husk mortar compositions of the invention whilst maintaining excellent bond strengths. Example 9 Series Ah. Rice husks variation in formula A

Example 10 Bond strength tests for compositions of Series Ah (rice husks content variation)

The mortar compositions of series Ah were mixed with water in the indicated ratio (composition: water). Sets of ceramic tiles were assembled with the wet mortar compositions of series Ah as described in Example 5. Results shown indicate the shear bond strengths (MPa) for tiles allowed to dry for 7 days (7d), 14 days (14d) and dried for 7 days and immersed in water for 7 days (7/7d) in accordance with Australian standard AS 2358, sections 3.2-3.4.

Example 10 shows variations in the quantity of rice husks which may be used in the mortar compositions of the invention whilst maintaining acceptable bond strengths.

In the Examples above reference is made to the following products:- Vinnapas (manufactured by Wacker Chemie, Germany); Omyacarb (Omya Southern, Bathurst New South Wales); Walocel (Wolff Walsrode, Germany); Elotex (Elotex, Switzerland); Methocel (Dow Chemical, USA); PVA PB 20S (Kuraray, Singapore); and Agitan P823 (Munzing Chemie, Germany).

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described without departing from the scope of the invention. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred or indicated in the specification, individually or collectively, and any and all combinations of any two or more of said steps or features. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour.

Claims

The claims defining the invention are as follows:

1. A mortar composition which comprises: a) 100 parts by weight of cement; b) 1-80 parts by weight of untreated rice husks; c) 30-200 parts by weight of one or more fillers and additives; and d) 0.2-10 parts by weight of an accelerator.

2. A mortar composition of claim 1 , wherein the cement is Portland cement.

3. A mortar composition of claim 1, wherein the accelerator is a C_1-4 carboxylic acid salt or a nitrate salt.

4. A mortar composition of claim 3, wherein the anion of the C_1-4 carboxylic acid salt is formate, acetate, propionate, oxalate or malonate.

5. A mortar composition of claim 3, wherein the counter ion of the C_1- carboxylic acid salt is calcium, magnesium, potassium, lithium, sodium or ammonium.

6. A mortar composition of claim 3, wherein the C_1-4 carboxylic acid salt is calcium formate, sodium formate or ammonium formate.

7. A mortar composition of claim 6, wherein the C_1- carboxylic acid salt is calcium formate.

8. A mortar composition of claim 3, wherein the counter ion of the nitrate salt is calcium, magnesium, potassium, lithium, sodium or ammonium.

9. A mortar composition of claim 3, wherein the nitrate salt is calcium nitrate.

10. A mortar composition of claim 3, wherein the accelerator is in an amount of 2-6 parts by weight.

11. A mortar composition of claim 1, wherein the untreated rice husks are predominantly in the size range of 100-600 microns.

12. A mortar composition of claim 11, wherein the untreated rice husks are predominantly in the size range of 150-500 microns.

13. A mortar composition of claim 1 , wherein the untreated rice husks are in an amount of 20-40 parts by weight.

14. A mortar composition of claim 13, wherein the untreated rice husks are in an amount of 30-35 parts by weight.

15. A mortar composition of claim 1, wherein the fillers and additives are in an amount of 30-150 parts by weight.

16. A mortar composition of claim 15, wherein the fillers and additives are in an amount of 45-120 parts by weight.

17. A mortar composition of claim 1, wherein the filler is an aggregate filler, a fine filler or a combination thereof.

18. A mortar composition of claim 17, wherein the filler includes silica or alumina materials such as fine or ground sand, ground silica, colloidal or precipitated silica, corundum and alumina trihydrate; limestone, volcanic aggregate, ground quartz, volcanic ash, fly ash, talc, pumice, clays, expanded clays, carbonates such as natural, ground or surface treated magnesium, barium or calcium carbonates such as marble dust or dolomite; sulfates such as calcium sulfate in the form of hydrated plaster and gypsum; insulation materials such as expanded glass or clays, mica, vermiculite, perlite and Celite; expanded plastics such as polystyrene and polyurethane; crumbed rubber; metal filings, short-milled fibres, expanded polystyrene beads, carbon beads, gravel, stones, fines, shale, other clean inert materials and mixtures thereof.

19. A mortar composition of claim 18, wherein the filler is fine sand.

20. A mortar composition of claim 19, wherein the fine sand in an amount of 25-150 parts by weight.

21. A mortar composition of claim 20, wherein the fine sand is predominantly in the particle size range of 150-500 microns.

22. A mortar composition of claim 1, wherein the additives include elastomeric or amorphous thermoplastic polymers as redispersable powders or dispersions including natural rubber, styrene butadiene, polyacrylonitrile butadiene, polychloroprene, polyvinylacetate, polystyrene, polyvinylchloride, polyacrylates, and their copolymers; ethylene/vinyl acetate copolymers and terpolymers; setting aids including calcium chloride, calcium sulfate and calcium nitrate; dispersants and surfactants including fatty amines, alkyl amines, ethylene oxide condensates, sulfonated soaps, sodium naphthalene formaldehyde sulfonates and sulfonated melamine formaldehydes; calcium salts such as calcium carbonate and hydrated lime; water soluble thickeners and colloids such as hydroxy alkyl cellulose ethers, hydroxy propyl methyl cellulose, hydroxy ethyl cellulose, ethyl hydroxyethyl cellulose, acrylamide modified polymers, starches, polysaccharides, xanthan gums, proteins, starches; animal glues; chlorinated paraffins, alkali metal fatty acid salts, alkylene glycols, polyvinyl alcohols, preservatives, antimicrobial agents, waterproofing agents, antifoaming agents and mixtures thereof.

23. A mortar composition of claim 22, wherein the additives include calcium carbonate in an amount of up to 25 parts by weight, hydroxy alkyl cellulose ethers in an amount of 0.1-3 parts by weight, ethylene/vinyl acetate copolymers in an amount of 0.1-10 parts by weight, polyvinyl alcohol in an amount of 0-10 parts by weight, and hydrated lime in an amount of 0-6 parts by weight.

24. A method of making a mortar composition comprising the step of mixing together in any order: a) 100 parts by weight of cement; b) 1-80 parts by weight of untreated rice husks; c) 30-200 parts by weight of one or more fillers and additives; and d) 0.2-10 parts by weight of an accelerator.

25. A mortar composition prepared by the method of claim 24.

26. A settable mortar composition which comprises: a) 100 parts by weight of cement; b) 1-80 parts by weight of untreated rice husks; c) 30-200 parts by weight of one or more fillers and additives; d) 0.2-10 parts by weight of an accelerator; and e) 30-150 parts by weight of water.

27. A settable mortar composition of claim 26, wherein the water is in an amount of 60-100 parts by weight.

28. A method of making a settable mortar composition comprising the step of mixing a mortar composition of claim 1 with 30-150 parts by weight of water to form a soft paste.

29. A method of fixing a tile to a supporting surface which method comprises trowelling a settable mortar composition of claim 26 onto the supporting surface, setting the tile into the mortar composition and allowing the mortar composition to set.

30. A mortar composition of claim 1 substantially as hereinbefore described especially with reference to the Examples.

31. A settable mortar composition of claim 26 substantially as hereinbefore described especially with reference to the Examples.