WO2020208401A1

WO2020208401A1 - Dry powder composition, composite and method for attenuating impact noise in a building

Info

Publication number: WO2020208401A1
Application number: PCT/IB2019/052932
Authority: WO
Inventors: Boon Kiat Lim; Tommy Kai Jing THAM
Original assignee: 3M Innovative Properties Company
Priority date: 2019-04-09
Filing date: 2019-04-09
Publication date: 2020-10-15

Abstract

An impact-noise attenuating composite, comprising: a cementitious layer, the cementitious layer comprising a mixture of hydraulic cement, fly ash, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious layer, the hollow glass microspheres having an average particle size of less than 100 mum and being present in an amount of between 1% to 10% by weight of the cementitious layer. A dry powder composition, comprising a mixture of hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious layer, the hollow glass microspheres having an average particle size of less than 100 mum, being present in an amount of between 0.01% to 15% of the total weight of the mixture. A method of attenuating impact-noise in a building, comprising forming a cementitious composition by combining water with the dry powder mixture, spreading the cementitious composition over a concrete floor or wall surface, or into a mold, allowing the cementitious composition to set.

Description

DRY POWDER COMPOSITION, COMPOSITE AND METHOD FOR

ATTENUATING IMPACT NOISE IN A BUILDING

TECHNICAL FIELD

[0001] The present disclosure generally relates to an impact-noise attenuating composite, dry powder compositions thereof, and methods of forming the composite.

BACKGROUND

[0002] Noise pollution is a common feature of high density urban areas. Categorizable into airborne noise and structure-borne noise, it is an important issue for city planners and developers to address on behalf of residents. Air-borne noise is the product of wide ranging factors extrinsic to a building, such as proximity to high-volume pedestrian or vehicular traffic, or temporary construction activities occurring in the area, whereas structure-borne noise is the product of human activities in the building that cause impact forces to be exerted on the wall or floor surfaces of the building. In particular, structure-borne noise, also known as impact noise, occurs in buildings as a result of usual day-to-day activities such as furniture being moved across the floor, items being dropped on the floor, drilling or hammering of nails into the wall, or mere heavy footed walking. The problem with impact noise is that it transmits readily across walls and floors, especially from one apartment to the apartment below, due to the fact that solid concrete is an efficient conductor of sound.

[0003] In order to reduce the transmission of impact noise across floors and walls, a variety of acoustic insulation methods based on noise absorption, deflection and/or vibrational isolation principles have been employed in the past. For example, acoustic sound proofing coverings, such as carpets or latex mats, may be used to absorb the impact of forces on floors and walls. Floating floors comprising a rigid finishing material supported on a resilient mat or pads may also be used.

[0004] The selection of acoustic insulation in buildings involve multi-faceted considerations, one of which is long-term structural safety. Materials used should be mechanically strong and chemically stable to provide for many years of use. From a cost perspective however, it is advantageous to avoid acoustic solutions that either require significant labor to install, or materials that are costly to manufacture.

[0005] In order to meet these different requirements, it is desirable to provide an all-in-one impact noise solution that effectively attenuates impact noise in a building, while being easy to install and cost-effective to manufacture. SUMMARY

[0006] The present disclosure describes an impact-noise attenuating composite comprising hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres in the composite, the hollow glass microspheres having an average particle size of less than 100 pm, density of less than 1 gram per cubic centimeter (g/cc), and are present in an amount of between 1% to 10% of the total weight of the composite.

[0007] In another aspect, the present disclosure describes a dry powder composition for forming an impact-noise attenuating composite, comprising: a mixture of hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent, the hollow glass microspheres having an average particle size of less than 100 pm, density of less than 1 gram per cubic centimeter (g/cc), and are present in an amount of between 1% to 10% of the total weight of the mixture.

[0008] In a further aspect, the present disclosure describes a method of forming an impact- noise attenuating composite, comprising providing a dry powder composition comprising: a mixture of hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent, the hollow glass microspheres having an average particle size of less than 100 pm, density of less than 1 gram per cubic centimeter (g/cc), and are present in an amount of between 1% to 10% of the total weight of the mixture, mixing the dry powder composition with water to form a slurry, casting the slurry onto a substrate, and allowing the slurry to dry to form the composite.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying figures. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present disclosure.

[0010] FIG. 1 shows a cross section of a composite according to an embodiment comprising hollow glass microspheres dispersed in a cementitious layer

[0011] FIG. 2 shows a cross section of a composite according to another embodiment comprising a viscoelastic layer and a cementitious layer.

[0012] FIG. 3 shows a cross section of a composite according to an embodiment comprising a viscoelastic layer and an embedded cementitious layer.

[0013] FIG. 4 shows a cross section of a composite comprising a viscoelastic layer and an embedded cementitious layer cast over in-situ concrete and precast concrete. [0014] FIG. 5 is a graph of compressive strength of screed samples with varying replacement rates of fine aggregates by hollow glass microspheres.

[0015] FIG. 6 is a graph of compressive strength of concrete samples with varying replacement rates of fine aggregates by hollow glass microspheres.

[0016] FIG. 7 is a graph of impact noise level (dB) measurements on screed samples.

[0017] FIG. 8 is a graph of impact noise level (dB) measurements on concrete samples.

DETAILED DESCRIPTION

[0018] The present disclosure is generally directed to composites suitable for providing impact noise attenuation on building surfaces that sustain impact forces. Typically, such surfaces include floor surfaces and walls in a building. Composites of the present disclosure comprise a cementitious layer obtained from a mixture of hydraulic cement, and aggregates, to which hollow glass microspheres (HGM) having an average particle size of less than 100 pm are added in an amount of between 0.01% to 15% of the total weight of the composite, along with a dispersing agent for dispersing the hollow glass microspheres within the composite.

[0019] A surprising finding is disclosed herein in which composites comprising HGM were found to possess impact noise attenuation properties, and can be used to form concrete as well as mortar and plasters. By incorporating suitable dispersing agents which disperse the HGM uniformly throughout the composite, composites of the present disclosure do not suffer from a significant loss of mechanical strength, as is typical when brittle or soft additives such as glass- based materials are added to the cementitious mixture. Hollow glass microspheres are generally spherical in shape and include a hollow center occupied by a gas, for example, air. By incorporating sufficient quantities of hollow glass microspheres into the composite, a significant volume of the composite becomes occupied by gas. It is thought that the vibrations from an impact force propagating through the composite lose energy more quickly than in a solid structure because some of the vibrations are transmitted to the gas molecules present in the composite. Kinetic energy gained by the gas molecules is partly dissipated as heat due to friction between the gas molecules and internal surfaces of the composite such as the walls of the hollow glass microspheres and the cementitious layer. The impact force thus becomes partially “absorbed” into the composite, thus attenuating the impact noise.

[0020] In the context of this description, the following terms shall have the following meaning:

[0021] “Composite” means materials derived from a mixture of two or more constituent substances that has been allowed to set and solidify. It may take the form of a solidified, homogenous mixture of individual constituents, or a multilayer arrangement of individual constituents, or a combination of a mixture of individual constituents and a multilayer arrangement of individual constituents.

[0022] “Cementitious” means having the properties of cement. Cementitious materials include any variety of material that has characteristics of cement and can thus be used as construction binder to bond the constituents of concrete or screed. It may include hydraulic cement (such as ordinary Portland cement), pozzolanic cement, rapid hardening cement, sulphate resisting cement, and high alumina cement. Generally, cement contains at least calcium oxide (limestone), silica, alumina and/or magnesia in varying amounts.

[0023] “Hollow glass microspheres” refer to generally spherical shaped glass microspheres having an aspect ratio of about 1 and a hollow, gas-filled centre.

[0024] Composites of the present disclosure may be used to provide impact noise attenuation on different building elements. For example, it may be formed as a layer of screed over a concrete floor slab, or as a layer of plaster over a wall surface, or it may be comprised in concrete substrate, such as pre-cast or in-situ concrete, in a building.

[0025] Hydraulic cement in the composite may comprise any suitable cement, including, for example, any suitable type of Portland cement such as ordinary Portland cement (OPC), Type I, Type II or Type V cement having sulfate resistance, rapid hardening cement Type III having high early strength, slow reacting low heat hydration Type IV cement, high alumina cement, or white cement. In preferred embodiments, hydraulic cement comprises OPC, which is in the form of a grey powder and is probably the most common and widely used cement in the construction industry. Its composition is generally comprised of 60 to 67% by weight lime (CaO), 17 to 25% silica (S1O2), 3 to 8% alumina (AI2O3) and iron oxide (Fe203) 0.5 to 6%.

[0026] Aggregates refer to any variety of construction aggregates, including fine aggregates comprising particles having a diameter smaller than 4.75 mm, coarse aggregates comprising particles having a diameter larger than 4.75 mm. Examples include gravel, crushed stone, slag and geosynthetic aggregates, for example.

[0027] Hollow glass microspheres (HGM) refer to glass beads having a hollow, generally spherical configuration surround by a thin glass shell In preferred embodiments, the HGMs comprise soda-lime / borosilicate glass. In other embodiments, HGMs comprise a ceramic.

Other materials used to manufacture HGMs include aluminosilicate glass microspheres. A variety of glass microspheres manufactured by 3M Company, such as type S38H, S60, S60HS, K46 and ΪM30K, may be used presently. HGMs may have a particle size of up to 1000 micron (pm). In the present application, a suitable average particle size is less than 100 pm. In some embodiments, HGMs have an average particle size between 10 pm to 50 pm. In various examples, the HGM have an average particle size of 44 pm (S38HS), or 30 pm (S60HS), 25 pm (S32HS), or 17 pm (ΪM30K).

[0028] Due to its thin shelled hollow configuration, HGMs may be broken by compression and shear forces. To maintain the structural integrity of the HGMs in the composite or during the manufacture of dry powder compositions for forming the composite, HGMs should be selected from those possessing a high isostatic crush strength value. In some embodiments, HGMs have an isostatic crush strength of at least 25 MPa (3,650), or at least 38 MPa (5,500 psi) (S38HS), or at least 69 MPa (10,000 psi) (S60), or preferably at least 124 MPa (18,000 psi) (S60HS), or more preferably at least 193 MPa (28,000 psi) (ΪM30K).

[0029] In general, the HGMs have a bulk density of less than 1 gram per cubic centimeter (g/cc). More preferably, the HGMs have a bulk density of between about 0.3 g/cc to 0.6 g/cc. In non-limiting examples, the HGMs have a bulk density of 0.32 g/cc (S32HS), 0.38 g/cc (S38HS), or 0.6 g/cc (S60HS).

[0030] The cementitious layer may comprise between 1% and 15% of HGMs by weight in some embodiments. In embodiments where coarse aggregates are present, such as in concrete, the amount of HGMs may range from about 1% to about 4% by weight of the cementitious layer. In embodiments where no coarse aggregates are present, such as when the in mortar, screed or plaster dry powder mixtures, the amount of HGMs may range from about 5% to about 15% by weight of the composite. Cement has a bulk density of about 3.15 g/cc, whereas HGMs have a bulk density of less than 1 g/cc, and in some embodiments a bulk density ranging from 0.32 to 0.6 g/cc. This means that HGMs have a bulk density value of between about 5 to 10 times lower than that of cement. This translates, in various embodiments, to HGMs being present in an amount, in a variety of embodiments, of about 10%, 20%, 30%, 40% or 50% of the volume of aggregate replacement. In other words, the ratio of the volume of hollow glass microspheres to the volume of aggregates present in the composite may be 1 :9, or 2:8, or 3:7, or 4:6, or 1 : 1. In preferred embodiments, the HGMs are present in an amount of between 30% to about 50% (i.e. 3:7 to about 1 : 1) by volume of aggregate replacement.

[0031] An important requirement for the use of the composite in concrete and mortar is a sufficiently high compressive strength. It was found that cementitious mixtures containing HGMs without adding suitable chemical admixtures resulted in materials that had diminished compressive strength. From empirical evidence, it was noticed that mixing the HGMs homogenously into a cementitious mixture in the aqueous phase presented a challenge because the HGMs tend to float to the surface and would eventually clump together, entrapping water within the composite. It is thought that this behavior affects the mechanical strength of the composite. Thus, to improve the compressive strength of the composite, the effective wetting of the low density, hydrophobic HGM in a high surface tension, water-borne system needs to happen in order for HGM dispersion to occur. It was presently found that dispersing agents may be used to disperse the HGMs homogenously into the cementitious mixture during mixing. The mechanism of dispersion of the HGMs in aqueous media is thought to be via repulsion of HGM particles, via adsorption of dispersing agent molecules that are either charged, steric, or a combination of both, onto the surface of the HGMs. Dispersing agent molecules break down the agglomeration of HGMs by causing repulsion between HGM particles. The dispersing agent may comprise a molecule having one end that is adsorbed onto to the surface of the HGM, and the other end comprises a steric, or a polar or charged group, or a combination of a steric and a polar/charged group (e.g. a charged oligomer surfactant) that remains soluble in the aqueous phase. Examples of dispersing agents include oligomeric or high molecular weight polymeric dispersants, such as polyacrylic acids, polyacrylates, and polyurethanes, with molecular weights ranging from 1,000 to 20,000 g/mol.

[0032] In preferred embodiments, the dispersing agent comprises a water soluble poly(urethane-acrylic) polymer comprising acrylic graft copolymer with a polyurethane backbone. Other examples of dispersing agents used herein include sulfonated melamines and sulfonated naphthalenes as well as lignosulfonates and polycarboxylates. Other examples include tripolyphosphate and hexametaphosphate. Other non-limiting examples of polymers that may be used include a silane coupling agent.

[0033] In general, any suitable chemical or mineral additive, also known as admixtures, may be added to the cementitious mixture to achieve a certain desired physical characteristic in the composite. Admixtures refer to ingredients other than hydraulic cement, water, and aggregate. For example, admixtures that are water reducing, retarding (increase setting time), accelerating (increase setting time), air entraining, pozzolanic, damp-proof, air detraining, may be added. Specific examples of admixtures include fly ash, blast furnace slag, silica fume, and/or gypsum. In certain embodiments, the composite may further include fly ash. Fly ash refers to a mineral admixture normally produced from burning anthracite or bituminous coal in coal-fired power plants, and has pozzolanic properties. Pozzolans are silicate-based materials that react with calcium hydroxide when water is added, producing calcium silicate hydrate which acts as a binder having properties similar to cement. Hence, fly ash can be used as a cement replacement, as well as to alter cement properties such as setting time, increase durability, reduce cost and reduce pollution, without significantly reducing the final compressive strength or other performance characteristics. Fly ash also includes fly ash-silica fume blends. Fly ash is used in the present application to increase workability and particle packing. Fly ash particles are generally spherical in shape and range in size from 0.5 pm to 300 pm. In some examples, Portland Pozzolana Cement (PPC) may be used in which pozzolanic materials such as fly ash is blended with ordinary portland cement (OPC).

[0034] The cementitious layer may further comprise suitable fillers for improving the compressive strength of the composite. In one embodiment, a reinforcing fiber filler is present in the composite. The reinforcing fiber filler comprises small, randomly distributed fibers embedded in the cementitious matrix. The function of the fiber is to increase the energy absorption capacity, which leads to flexural toughness. A non-limiting example of a reinforcing fiber filler comprises discontinuous discrete fibers. In a preferred embodiment, the reinforcing fiber filler comprises polyvinyl alcohol fibers. Other examples include steel fibers. More recent examples include cellulosic waste such as rice husk, saw dust and waste plastic, which enable waste materials to be recycled into to concrete and mortar. In some embodiment, limestone fillers may also be used. The limestone enhances hydration of the hydraulic cement, leading to improved mechanical strength.

[0035] Viscoelastic material may be incorporated into the composite to achieve improved impact noise attenuation performance. In an embodiment, viscoelastic particles are dispersed homogeneously in the cementitious layer. Examples of viscoelastic particles include rubber granules. The elastic nature of the rubber granules provides excellent impact force absorption. The rubber granules may be hydrolyzed by surface treatment with an alkali or a silane coupling agent.

[0036] Viscoelastic material may alternatively be incorporated in a layer arrangement with the cementitious layer. In a preferred embodiment, a viscoelastic layer may be arranged adjacent to the cementitious layer in the composite. The viscoelastic layer may also be embedded in the cementitious layer. A multilayer arrangement comprising an alternating arrangement of viscoelastic layers and cementitious layers may also be used to achieve better noise impact attenuation. Examples of usable viscoelastic materials include amorphous polymers, semi crystalline polymers, biopolymers and bitumen. In a preferred embodiment, the viscoelastic layer may comprise a foam, e.g., a polymer foam selected from the group consisting of polyurethane, polyvinyl chloride and polyethylene. In a particular embodiment, the viscoelastic layer comprises an adhesive foam tape.

[0037] In some embodiments where the composite is formed as screed, the cementitious layer may comprise, by percentage of its total weight, 15 to 25% hydraulic cement, 1 to 10% fly ash, 40 to 65% fine aggregates, 5% to 12% hollow glass microspheres, 0.1% to 2% dispersing agent, and less than 5% fillers and additives. In some embodiments where the composite is formed as concrete, e.g., as a concrete substrate, it may comprise, by percentage of the total weight of the composite, 17 to 20% hydraulic cement, 1 to 10% fly ash, 20 to 35% fine aggregates, 30 to 40% coarse aggregates, 1% to 4% hollow glass microspheres, 0.1 to 2% dispersing agents, and less than 5% fillers and additives.

[0038] A dry powder composition may be provided as a ready-mix product for forming an impact-noise attenuating composite of the present disclosure. Ready mix bags are suitable for small quantity applications and may be conveniently carried by home users intending to carry out small scale installations at home. The ready mix dry powder composition comprises a mixture of hydraulic cement, fly ash, aggregates and hollow glass microspheres. The dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious layer may be included as part of a kit as a separate liquid additive alongside the dry powder. The dispersing agent may alternatively be included in the ready mix in the form of a dry powder. The hydraulic cement, fly ash, aggregates and hollow glass microspheres may also be provided separately in a kit, i.e. in separate bags, to be mixed on site.

[0039] In some embodiments, the hollow glass microspheres (HGMs) in the dry powder composition have an average particle size of less than 100 pm. In some embodiments, the HGMs may be present in an amount of between 1% to 15% of the total weight of the mixture. Depending on the application, in certain embodiments, the dry powder composition comprises between 30% to 50% by volume of hollow glass microspheres. The dry powder composition may preferably comprise soda lime borosilicate hollow glass microspheres. The HGMs may have an average particle size of between 20 to 50 pm. The HGMs may also have a bulk density of between about 0.3 grams per cubic centimeter (g/cc) to 0.6 g/cc. The HGMs may also have an isostatic crush strength of at least 34 MPa (5000 psi).

[0040] For screed or mortar applications, the ready mix dry powder composition may comprise, by weight percentage of the composition, 15 to 25% hydraulic cement, 1 to 10% fly ash, 40 to 65% fine aggregates, 5 to 12% hollow glass microspheres, 0.1% to 2% dispersing agent, and less than 5% fillers and additives. For concrete applications, the ready mix dry powder composition may comprise, by weight percentage of the composition, 17 to 20% hydraulic cement, 1 to 10% fly ash, 20 to 35% fine sand aggregates, 30 to 40 coarse sand aggregates, 1 to 3% hollow glass microspheres, 0.1% to 2% dispersing agent, and less than 5% fillers and additives.

[0041] For large scale projects, the composite may be formed on site directly without the use of ready mix dry powder compositions. The present disclosure provides for a method of attenuating impact-noise in a building, comprising: forming a cementitious composition by combining water with dry powder mixture of hydraulic cement, fly ash, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious composition, spreading the cementitious composition over a concrete floor or wall surface, or into a mold, and allowing the cementitious composition to set. In some embodiments, the hollow glass microspheres having an average particle size of less than 100 pm. In some embodiments, the hollow glass microspheres are present in an amount of between 1% to 15% of the total weight of the mixture

[0042] The amount of water to be added typically depends on the amount of hydraulic cement present, as well as the chemical admixtures present which may reduce the water requirement. In certain embodiments, the ratio of the weight of water added to the weight of hydraulic cement present is between 0.3 to 0.5. In other words, for every 100 kg of hydraulic cement, about 30 kg to 50 kg of water is added.

[0043] In embodiments where a viscoelastic layer is present, the viscoelastic layer may first be formed as an underlay over the concrete floor or wall surface to be provided with impact noise insulation. Subsequently, the cementitious composition is spread over the viscoelastic layer. In specific embodiments, the viscoelastic layer comprises a foam material, e.g., a foam materials selected from the group consisting of polyurethane, polyvinyl chloride and

polyethylene.

[0044] Non-limiting examples of the application of the composites over a surface to be provided with impact noise insulation will now be described. FIG. 1 shows impact noise attenuating composite 10 of the present disclosure comprising a cementitious layer 20 arranged over a substrate 60. Hollow glass microspheres 22 are dispersed throughout the cementitious layer 20. Examples of substrate 60 include in-situ concrete floor surface, pre-cast concrete floor surface, a hollow block wall surface and a brick wall surface, and the like. For floor surfaces, the composite 10 may be provided as screed over in-situ or precast concrete floor substrates, with homogeneous or porcelain tiles 50 arranged over the composite 10. respectively. For wall surfaces, tiles 50 are absent, and composite 10 may be provided as a plaster of thickness between 1 mm to 10 mm thick over the wall surface.

[0045] FIG. 2 shows an embodiment in which composite 10 comprises cementitious layer 20 and an adjacent viscoelastic layer 30. Viscoelastic layer 30 is interposed between the substrate 60 and the cementitious layer 20. The viscoelastic layer 30 may comprise viscoelastic tape having adhesive on one side and is first laid over the surface of the substrate 60, and then the composite 10 is cast over the tape. FIG. 3 shows yet another embodiment, in which composite 10 comprises cementitious layer 20, and an embedded viscoelastic layer 30 within the cementitious layer 20.

[0046] In a multistory building such as a residential apartment, separate in-situ concrete and precast concrete layers may be used. Screed, in-situ concrete and precast concrete layers may typically be provided with thicknesses of about 50 mm, 80 mm and 70 mm, respectively. FIG. 4 shows an embodiment wherein composite 10 comprises cementitious layer 20 and an embedded viscoelastic layer 30 within the cementitious layer 20 and having thickness of about 50 mm and is arranged over an in-situ concrete layer 62 having thickness of about 80 mm, and beneath it a precast concrete slab 64 having thickness of about 70 mm. Accordingly, in embodiments where it is used as a screed, composite 10 can have an overall thickness of between 40 mm to 60 mm, while the substrate 60 may have a thickness of between about 50 mm to 150 mm.

[0047] The following examples illustrate some embodiments and aspects of the invention. It will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be performed without altering the spirit or scope of the invention, and such modifications and variations are encompassed within the scope of the invention as defined in the claims which follow. The following examples do not in any way limit the invention.

Example 1: Preparation and comparison of screed mixtures

[0048] Different screed mixtures were prepared with varying amounts of individual constituents in accordance with the following weight ranges:

(i) Cement (17.5-24%)

(ii) Fly ash (7.5-10% - corresponding to 30% volume replacement of cement)

(iii) Fine aggregate (41-63%)

(iv) Hollow glass microspheres, abbreviated“HGM” (5-9.3% - corresponding to 30-50% volume replacement of fine aggregates by volume)

(v) Water/bi nder (w/b) ratio of 0.5

(vi) Dispersing agent comprising urethane acrylate oligomers (obtainable from Alfa Chemicals) abbreviated“DA” (corresponding to 0.8-1.1% by volume of cement present).

Example“S0BG” acted as the control with no HGM content present. No reinforcing fiber filler was used.

[0049] Fly ash present was kept at 30% by volume of the total cement content. Mixtures incorporating HGM levels of 30%, 40% and 50% by volume replacement of fine aggregates were prepared. The water to cement (binder) weight ratio (w/b) was kept at 0.5 for sufficient workability, accompanied by a DA content of 0.8-1.1% of the volume of cement present. Fibers were not included in this particular mix design to observe the direct effects of HGMs replacement of fine aggregates on the strength of screed samples. The detailed mixture proportions are shown in Table 3.

Table 3: Screed mixtures (kg/m3)

[0050] Compressive strength: The compressive strength results of all screed samples cured for up to 28 days are shown in FIG. 5. All samples reached over 20 MPa after 14 days of curing. Although the high surface area of HGMs resulted in low initial compressive strengths at 1 day (~1 MPa) when compared with the control mix S0HGM (~10 MPa), the inclusion of BG380 and BG600 at 30% and 40% replacement rates produced similar performance as the control mix at 3 days (13-14 vs. 16 MPa). Despite initial low strengths, samples with 30-40% replacement of BG600 reached the same strength as that of the control mix (~31 MPa) at 14 days.

Corresponding strengths of samples containing BG380 were slightly lower and ranged between 25-27 MPa. The replacement of 50% of aggregates by HGM led to the reduction of the 14-day compressive strength by 5 and 7 MPa within samples S50BG600 and S50BG380 when compared to the control sample, respectively. Due to their higher surface areas, screed samples involving the use of BG380 produced lower 28-day strengths than those with BG600. While increasing replacement rates resulted in lower 28-day strengths, sample S30BG600 achieved 28- day strengths equivalent to those of the control sample. This sample highlights the potential of using HGMs at a 30% replacement of fine aggregates without compromising performance.

[0051] Water absorption: The water absorption values of all screed mixes cured for 14 and 28 days are listed in Table 4. The water absorption values of all samples generally decreased with increasing curing duration (i .e. from 14 to 28 days) due to the formation of hydrate phases that filled in the initially available pore space. When compared with the control sample, samples involving the replacement of BG600 revealed lower water absorption values, indicating a denser structure that could be facilitated by the pore filling effect of BG600.

[0052] The introduction of BG380 led to higher water absorption values than the control sample, possibly due to the challenges present in dispersing BG380 particles within the designed formulations. The uneven dispersion of BG380 was associated with their high surface area and low density, which reduced the overall bonding strength. Unlike BG380, BG600 particles increased the density of the formulations they were included in, thereby displaying lower water absorption values than all other samples.

Table 4: Water absorption of screed samples

[0053] Bulk density: The bulk density values of screed samples measured at 14 and 28 days are listed in Table 5. The final bulk density value of the control sample was around 2.3 kg/m3, whereas those involving the use of HGM ranged between 1.6 and 1.9 kg/m3. The replacement of sand with low density HGM resulted in the reduction of the bulk density values of the screed samples by 15-29%. An increase in the replacement rate led to higher reductions in the bulk densities, as expected, whereas the curing duration did not have a major influence on the density values.

Table 5: Bulk density of screed samples

[0054] Thermal conductivity: The thermal conductivity values of all screed samples cured for 14 and 28 days are listed in Table 6. A notable decrease in the thermal conductivity was observed in all samples, which decreased with an increase in the amount of BG. The 14-day thermal conductivity of the control sample was 2.6 W/mK, whereas this value was reduced by around 60% with the replacement of fine aggregates with hollow glass microspheres, resulting in values as low as 1.0 W/mK. This reduction was associated with the lower conductivity of the hollow glass microspheres in comparison to the other cementitious materials used in the control sample. Another factor influencing thermal conductivity was the curing duration, an increase in which led to lower values. The thermal conductivity values obtained by all samples containing the same replacement levels of BG380 and BG600 did not differ much from each other, albeit those with BG380 revealed slightly lower values. This could be associated with the lower densities of BG380 samples, revealed by their higher water absorption values.

Table 6: Thermal conductivity of screed samples (W/mK) Example 2: Preparation and comparison of concrete mixtures

[0055] Different concrete mixtures were prepared in accordance with the following weight ranges:

(i) Cement (-17.6-19.9%)

(ii) Fly ash (-4.4-4.9% - corresponding to 20% replacement of cement by volume)

(iii) Fine aggregate (-22.8-34%)

(iv) Hollow glass microspheres, abbreviated“HGM” (1.0-3.4% - corresponding to 20-40% replacement of fine aggregate by volume)

(v) Coarse aggregate (-34-38.5%)

(vi) Water/Binder (w/b) of 0.45

(vii) Dispersing agent comprising urethane acrylate oligomers (obtainable from Alfa Chemicals) (“DA”, corresponding to 0.8-1.2% of cement volume)

Example“C0BG” was used as the control with zero HGM content. No reinforcing fiber filler was used.

[0056] HGM replacement levels of 20%, 30% and 40% were used in this example. The water to cement (binder) weight ratio w/b was kept constant at 0.45 for sufficient workability, accompanied by a DA content at 0.8-1.2% of cement volume. The detailed mixture compositions are shown in Table 7.

Table 7: Prepared concrete mixes (kg/m3)

[0057] Compressive strength: The compressive strength results of all concrete samples cured for up to 28 days are shown in Figure 6. A steady strength development associated with the formation of hydrate phases was observed in all samples over the 28 days of curing, while a majority of the strength gain was observed within the first 14 days. Despite their initially low strengths, all samples involving the use of hollow glass microspheres reached a structural strength of >25 MPa after 14 days. Samples C20BG600 and C30BG600 achieved higher 28-day strengths than the control sample (i.e. 58 and 51 vs. 46 MPa). Although increasing the HGM replacement rate resulted in lower strengths, sample C40BG600 reached a similar 28-day strength as the control sample (46 MPa). The replacement of fine aggregates with BG380 that possessed a higher surface area led to a reduction in the strength of concrete samples. Although sample C20BG380 produced an equivalent 28-day strength with the control sample, an increase in the HGM replacement rate within samples C30BG380 and C40BG380 revealed 35 MPa, which was 22% lower than the strength of the control sample. The results show the advantageous use of BG600 at up to 40% replacement rate without compromising the performance of the designed concrete formulations. An equivalent outcome was also observed within samples involving 20% replacement of fine aggregates by BG380.

[0058] Water absorption: The water absorption values of concrete samples after 14 and 28 days of curing are listed in Table 8. Compared to the control sample, the replacement of fine aggregates by BG380 and BG600 generally led to an increase in water absorption. This increase was consistent with the corresponding measurements performed on screed samples, where samples involving the use of BG380 revealed higher values than the control sample. These increases were generally associated with the physical properties of the HGM, which increased the overall porosity of the samples they were included in.

Table 8: Water absorption in concrete samples [0059] Bulk density: The bulk density values of concrete samples measured at 14 and 28 days are listed in Table 9. The final bulk density value of the control sample was around 2.3 kg/m3, whereas those involving the use of HGM ranged between 2.1 and 2.2 kg/m3. The replacement of sand with low density HGM resulted in the reduction of the bulk density values of the screed samples by 4-12%. An increase in the replacement rate led to higher reductions in the bulk densities, albeit at a lower rate than those observed in screed samples, which could be associated with the lower replacement rates utilized within concrete samples.

Table 9: Bulk density of concrete samples

[0060] Thermal conductivity: The thermal conductivity values of all concrete samples are listed in Table 10. Similar to the screed samples, a reduction in thermal conductivity was observed with the introduction of BG380 and BG600 into concrete formulations. While 14- and 28-day thermal conductivity of the control sample was 2.4 W/mK, the use of HGM led to 13- 38% lower 28-day thermal conductivity values ranging between 1.6 and 1.9 W/mK. The degree of this reduction was directly proportional to the replacement rate of fine aggregates with BG, increasing with higher HGM contents. When the two different types of HGM were compared, at replacement rates higher than 20%, the use of BG380 led to lower thermal conductivity values than samples involving the use of BG600. This difference was associated with the variations in the densities of the two HGM types, in which BG380 possessed lower densities. Another factor that influenced thermal conductivity was the duration of curing, which led to reduced values with increasing durations.

Table 10: Thermal conductivity of concrete samples (W/mK) [0061] Acoustic attenuation: In order to determine the effectiveness of the composite in attenuating impact noise, field and laboratory measurements in accordance with ISO 140 part VI, VII, and VIII (1998), ASTM E-492, and ASTM E-1007 were used. Impact noise measurements were made using a tapping machine placed on the test floor, and recording microphones were set up in the room immediately below the test floor. The measurement room was completely enclosed to exclude external ambient noise.

[0062] Ambient noise level was first measured before the experiment, followed by a baseline measurement using a commercially available screed (Davco™ Floor Screed ECO) comprising Ordinary Portland cement, recycled material, graded sand and various chemical additives, without any hollow glass microsphere particles. Test samples were selected from the layout based on FIG. 1 in which the composite comprised a single cementitious layer. Screed mixtures described in Example 1 were used. The composite test samples measured 50 mm thick. The results are shown in FIG. 7. HGM content at 50 vol% replacement provided superior impact noise attenuation of about 5 dB, dropping from 79 dB to 74 dB, compared to 30 vol%

replacement by HGM.

[0063] In a second test, a test sample was selected from the layout based on FIG. 3 in which the composite comprised a cementitious layer and an embedded viscoelastic layer. A 5.5mm thick low density viscoelastic foam layer (3M™ 4504 Vinyl Foam tape) was embedded within a cementitious layer of 30 vol% HGM of S38 type in accordance with the formulations described in Example 1. A baseline control measurement was made on a commercially available screed (Davco™ Floor Screed ECO) comprising Ordinary Portland cement, recycled material, graded sand and various chemical additives, without any hollow glass microsphere particles. The test results are shown in FIG. 8. The composite comprising a cementitious layer and an embedded viscoelastic layer provided the best impact noise attenuation. As the data shows, a reduction of impact noise from 79 dB to about 72 dB was achieved over the control.

[0064] Various embodiments and implementation of the present disclosure have been disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation. The implementations described above and other implementations are within the scope of the following claims. One skilled in the art will appreciate that the present disclosure can be practiced with embodiments and implementations other than those presented herein. Those having skill in the art will appreciate that many changes may be made to the details of the above- described embodiments and implementations without departing from the underlying principles thereof. The scope of the present application should, therefore, be determined only by the following claims.

Claims

1. An impact-noise attenuating composite, comprising:

a cementitious layer, the cementitious layer comprising a mixture of hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious layer, the hollow glass microspheres having an average particle size of less than 100 pm and being present in an amount of between 1% to 10% by weight of the cementitious layer.

2. The composite of claim 1, wherein the hollow glass microspheres comprise soda lime borosilicate hollow glass microspheres.

3. The composite of claim 1 or 2, wherein the hollow glass microspheres have an average particle size of between 20 to 50 pm.

4. The composite of any of claims 1 to 3, wherein the hollow glass microspheres have a bulk density of between about 0.3 grams per cubic centimeter (g/cc) to 0.6 g/cc.

5. The composite of any of claims 1 to 3, wherein the hollow glass microspheres have a isostatic crush strength of at least 25 MPa (3,650 psi).

6. The composite of any of claims 1 to 5, wherein the ratio of the volume of hollow glass microspheres to the volume of aggregates present is between 1 : 1 and 1 :4.

7. The composite of any of claims 1 to 6, wherein the dispersing agent is selected from the group consisting of a charged oligomer surfactant, silane coupling agent, and a water soluble polymer.

8 The composite of any of Claims 1 to 7, the cementitious layer further comprising fly ash

9. The composite of any of Claims 1 to 8, the cementitious layer further comprising a reinforcing fiber filler.

10. The composite of claim 9, wherein the reinforcing fiber filler comprises polyvinyl alcohol fibers.

11. The composite of any of claims 1 to 10, further comprising viscoelastic particles dispersed in the cementitious layer.

12. The composite of any of claims 1 to 11, wherein the cementitious layer is formed as a layer of screed over a floor surface.

13. The composite of any of claims 1 to 11, wherein the cementitious layer is formed as a layer of plaster over a wall surface.

14. The composite of claim 12 or 13, further comprising a viscoelastic layer arranged adjacent to the cementitious layer.

15. The composite of claim 14, wherein the viscoelastic layer is embedded in the cementitious layer.

16. The composite of claim 14 or 15, wherein the viscoelastic layer comprises a foam selected from the group consisting of polyurethane, polyvinyl chloride and polyethylene.

17. The composite of any of claims 12 to 16, wherein the cementitious layer comprises by percentage of its total weight,

15 to 25% hydraulic cement,

1 to 10% fly ash,

40 to 65% fine aggregates,

5 to 10% hollow glass microspheres,

0.1% to 2% dispersing agent, and

less than 5% fillers and additives,

wherein the sum total of the percentages adds up to 100%.

18. The composite of claims 1 to 11, wherein the cementitious layer is formed as a concrete substrate.

19. The composite of claim 18, wherein the concrete substrate comprises by percentage of the total weight of the composite,

17 to 20% hydraulic cement,

0 to 10% fly ash, 20 to 35% fine aggregates,

30 to 40% coarse aggregates,

1 to 4% hollow glass microspheres,

0.1 to 2% dispersing agents, and

0 to 5% fillers and additives,

wherein the sum total of the percentages adds up to 100%.

20. A dry powder composition for forming an impact-noise attenuating composite, comprising: a mixture of hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious layer, the hollow glass microspheres having an average particle size of less than 100 pm, being present in an amount of between 0.01% to 15% of the total weight of the mixture.

21. The composition of claim 20, wherein the hollow glass microspheres comprise soda lime borosilicate hollow glass microspheres.

22. The composition of claim 20 or 21, wherein the hollow glass microspheres have an average particle size of between 20 to 50 pm.

23. The composition of any of claims 20 to 22, wherein the hollow glass microspheres have a bulk density of between about 0.3 grams per cubic centimeter (g/cc) to 0.6 g/cc.

24. The composition of any of claims 20 to 23, wherein the hollow glass microspheres have an isostatic crush strength of at least 25 MPa (3,650 psi).

25. The composition of any of claims 20 to 24, wherein the ratio of the volume of hollow glass microspheres to the volume of aggregates present is between 1 : 1 and 1 :4.

26. The composition of any of claims 20 to 25, wherein the mixture comprises:

15 to 25% hydraulic cement,

0 to 10% fly ash,

40 to 65% fine aggregates,

5 to 10% hollow glass microspheres,

0.1% to 2% dispersing agent, and

0 to 5% fillers and additives, wherein the sum total of the percentages adds up to 100%.

27. The composition of any of claims 20 to 25, wherein the mixture comprises:

17 to 20% hydraulic cement,

0 to 10% fly ash,

20 to 35% fine sand aggregates,

30 to 40% coarse sand aggregates,

1 to 4% hollow glass microspheres, and

0.1% to 2% dispersing agent, and

0 to 5% fillers and additives,

wherein the sum total of the percentages adds up to 100%.

28. A method of attenuating impact-noise in a building, comprising

forming a cementitious composition by combining water with dry powder mixture of hydraulic cement, aggregates, hollow glass microspheres and a dispersing agent for dispersing the hollow glass microspheres uniformly in the cementitious composition, the hollow glass microspheres having an average particle size of less than 100 pm, and being present in an amount of between 1% to 15% of the total weight of the mixture,

spreading the cementitious composition over a concrete floor or wall surface, or into a mold,

allowing the cementitious composition to set.

29. The method of claim 28, wherein the ratio of the weight of water added to the weight of hydraulic cement present is between 0.3 to 0.5.

30. The method of claim 29, further comprising first forming a viscoelastic layer over the concrete floor or wall surface, then spreading the cementitious composition over the viscoelastic layer.

31. The method of claim 30, wherein the viscoelastic layer comprises a foam material selected from the group consisting of polyurethane, polyvinyl chloride and polyethylene.