GB2457297A

GB2457297A - A method of production of a masonry unit, a masonry unit, and a structure formed therefrom

Info

Publication number: GB2457297A
Application number: GB0802446A
Authority: GB
Inventors: John Paul Forth; Salah Zoorob
Original assignee: University of Leeds
Current assignee: University of Leeds
Priority date: 2008-02-09
Filing date: 2008-02-09
Publication date: 2009-08-12
Also published as: GB0802446D0; WO2009098481A1

Abstract

A method for producing a construction element comprises forming a mixture of a bituminous binder with a course aggregate, compacting said mixture at a compaction level of up to around 7 MPa, and at least partially curing the compacted mixture. A second method for producing a masonry unit comprises forming a mixture containing a graded aggregate and around 6 wt % of a bituminous binder, compacting the mixture, and at least partially curing the compacted mixture. A third method comprises forming a mixture containing a graded aggregate and a bituminous binder, compacting the mixture, and at least partially curing the compacted mixture by heating the compacted mixture to a temperature of around 200 {C. A masonry structure comprising a plurality of masonry units and a mortar, at least one of said masonry units comprising a graded aggregate and a bituminous binder is also disclosed.

Description

-1 2457297

A METHOD FOR PRODUCING A MASONRY UNIT AND A MASONRY

STRUCTURE FORMED FROM SAID MASONRY UNIT

The present invention relates to methods for producing masonry units, particularly, but not exclusively, environmentally friendly masonry units, and masonry structures formed from said masonry units.

The developed world has a major problem -it is running out of space to store all of the rubbish it creates. The current trend for land-filling is simply unsustainable. By way of example, in March 2005 it was estimated that the UK had 6 years disposal capacity remaining at current rates of tipping (Environment Agency 2005). In Europe, the situation is similar with high prices and taxes levied on material sent to landfill. The EU Landfill Directive has set stringent and demanding targets on all EU countries for reducing material sent to landfill (The Waste Thematic Strategy 2005).

A significant need therefore exists for a novel construction/masonry unit which could significantly contribute to the increased need for recycling; reduction in demand for natural aggregate extraction; reduction in waste sent to landfill; and/or the UK's 2016 zero-carbon new homes target (Communities and Local Government 2006). An object of the present invention is to address the above need.

According to a first aspect of the present invention there is provided a method for producing a masonry unit, the method comprising forming a mixture containing a bituminous binder and a graded aggregate containing a coarse aggregate fraction, compacting the mixture at a compaction level of up to around 7 MPa, and at least partially curing the compacted mixture.

The present invention provides a method for producing a masonry unit, hereinafter referred to generically as "Bitublock", which can be composed entirely of recycled/waste aggregates and binding agents from selected waste bitumens. As such, it could significantly contribute to a reduction in material sent to landfill. The performance of Bitublock has been shown to be at least equivalent to concrete block masonry products found in the UK. The present application describes the long-term behaviour of Bitublock masonry. These results have also been used to confirm the successful encapsulation of the recycled material by the bitumen binder. The masonry did not exhibit any enlarged expansion (cryptoflorescence) which results from chemical interaction between the mortar and Bitublock.

Bitublock readily satisfies all the physical and strength requirements of current coarse aggregate concrete block units manufactured in the UK but does not necessarily need to incorporate any natural aggregates and does not require any specifically manufactured or synthetic binders. Instead the new unit, Bitublock, can, if desired, incorporate only recycled aggregates. Bitublock is a masonry unit which may be composed entirely of recycled and waste aggregates and binding agents from selected commercially available and waste bitumens. Previously, the physical properties of Bitublock units composed of mixtures of incinerated sewage sludge ash, incinerated bottom ash, furnace bottom ash, fly ash, construction demolition waste, crushed glass, soil, rice husk ash, steel slag and compacted at pressures of above 8MPa have been reported (Forth et al 2006, Thanaya et al 2006). While this earlier work presented important initial results, further optimisation of Bitublock and its method of production were required and form the basis of the various aspects of the present invention.

The aggregate materials used in the specific embodiments described below were: steel slag (in 2002 the volume of production of metallurgical slags such as basic oxygen steel slag was I million tormes; only a fifth of this was recycled); crushed glass (glass collection has increased to meet the 2006 packaging targets of 60% resulting in an excess of 300,000-400,000 tonnes of green glass) and fly ash (currently 6 million tormes of fly ash are produced each year in the UK -only 40 to 50% of this is utilised), (Forth et al 2006).

The present application also reports the creep and moisture movement strain recorded on 7 course high by 4 brick wide single leaf Bitublock masonry structure constructed using a Class ii; 1: /2: 4 V2, cement: lime: sand mortar.

A second aspect of the present invention provides a method for producing a masonry unit, the method comprising forming a mixture containing a graded aggregate and around 6 wt % of a bituminous binder, compacting the mixture, and at least partially curing the compacted mixture.

A third aspect of the present invention provides a method for producing a masonry unit, the method comprising forming a mixture containing a graded aggregate and a bituminous binder, compacting the mixture, and at least partially curing the compacted mixture by heating the compacted mixture to a temperature of around 200 C. A fourth aspect of the present invention provides a masonry unit produced according to the first, second or third aspects of the present invention.

A fifth aspect of the present invention provides a masonry structure comprising a plurality of masonry units and a mortar, at least one of said masonry units comprising a graded aggregate and a bituminous binder.

The term "coarse aggregate" is used herein to refer to aggregate having a maximum nominal particulate size of around 14 mm and a minimum retained particulate size of 2.36 mm. The term "fine aggregate" is used herein to refer to aggregate having a minimum retained particulate size of 2.36 to 0.075 mm.

While any desirable compaction level, of up to around 7 MPa can be used, it is preferred that the compaction level is around 0.5 to 5 MPa. More preferably the compaction level is around I to 4 MPa. Most preferably the compaction level is around 2 MPa.

Compaction may be conducted in any desirable manner, although it is preferred that the mixture of the bituminous binder and the graded aggregate is compacted within a mould, shaped to provide the mixture with the desirable shape of the final masonry unit.

In a preferred embodiment, the mixture comprises up to around 10 wt % bituminous binder, more preferably around 1 to 8 wt % bituminous binder, still more preferably around 3 to 7 wt % bituminous binder, and yet more preferably around 5 to 7 wt % bituminous binder. It is more preferred that the mixture comprises around 6 wt % bituminous binder.

The mixture containing the graded aggregate may include one or more types of bituminous binder in any desirable ratio. In a preferred embodiment, the mixture comprises 50 penetration grade bitumen.

Preferably the graded aggregate contains around 20 to 60 wt % of the coarse aggregate fraction. More preferably the graded aggregate contains around 30 to 50 wt % of the coarse aggregate fraction. Most preferably the graded aggregate contains around 40 wt % of the coarse aggregate fraction.

Any appropriate coarse aggregate may be employed in the method representing the first aspect of the present invention and related aspects of the present invention. The coarse aggregate may, for example, comprise at least one of steel slag and crushed glass.

It is preferred that the mixture of the graded aggregate and the bituminous binder is produced by heating and mixing the graded aggregate and the bituminous binder.

Preferably said heating is effected before the graded aggregate and the bituminous binder are mixed together. At least one of the graded aggregate and the bituminous binder is preferably heated to a temperature of up to around 200 °C, and more preferably heated to a temperature of around 160 to 180 °C. It is preferred that the graded aggregate is heated to a temperature of up to around 200 °C, more preferably to a temperature of around 170 to 190 °C, and most preferably to a temperature of around C. The bituminous binder may be heated to a temperature of up to around 180 °C, more preferably to a temperature of around 150 to 170 °C, and most preferably heated to a temperature of around 160 °C. Heating of the graded aggregate and/or bituminous binder may be effected over any desirable time period. At least one of the graded aggregate and bituminous binder may be heated for a time period of up to around 5 hours, around 1 to 4 hours, or around 3 hours.

It is preferred to at least partially or fully cure the compacted mixture of graded aggregate and bituminous binder. The at least partial curing of the compacted mixture is effected by heating the compacted mixture to a temperature of up to around 250 °C, more preferably, around 80 to 240 °C, and still more preferably around 150 to 230 °C.

At least partial curing may be achieved by heating the compacted mixture to a temperature of around 180 to 220 °C, more preferably around 190 to 210 °C, and most preferably around 200 °C. At least partial curing of the mixture of graded aggregate and bituminous binder may be effected over any appropriate time period to provide an end product, i.e. a masonry unit, having the desired properties. Said at least partial curing of the compacted mixture may be effected by heating the compacted mixture for a time period of up to around 72 hours, a time period of around 1 to 48 hours, a time period of around 12 to 36 hours, and most preferably a time period of around 24 hours.

The above-defined fifth aspect of the present invention provides a masonry structure comprising a plurality of masonry units and a mortar, at least one of said masonry units comprising a graded aggregate and a bituminous binder.

Preferably the at least one of said masonry units comprises up to around 10 wt % bituminous binder, more preferably around I to 8 wt % bituminous binder, more preferably around 3 to 7 wt % bituminous binder, still more preferably around 5 to 7 wt % bituminous binder, and most preferably around 6 wt % bituminous binder. Any desirable bituminous binder or combination of binders may be used, although a particular suitable binder comprises 50 penetration grade bitumen.

It a preferred embodiment of the fifth aspect of the present invention the graded aggregate comprises a coarse aggregate. Preferably the graded aggregate contains around 20 to 60 wt % of the coarse aggregate, more preferably around 30 to 50 wt % of the coarse aggregate, and most preferably around 40 wt % of the coarse aggregate. Any suitable coarse aggregate may be employed, such as steel slag and/or crushed glass.

Preferably the graded aggregate employed in any of the above-defined five aspects of the present invention comprises around 80 to 40 wt % of a fine aggregate, more preferably around 70 to 30 wt % of a fine aggregate, and most preferably around 50 wt % of a fine aggregate. The fine aggregate can be chosen to suit a particular application.

By way of example, the fine aggregate may comprise crushed glass.

Taking in to account the amounts of coarse and/or fine aggregates contained in the graded aggregate, the graded aggregate may comprise any appropriate amount (e.g. up to around 10 %) of a filler material, such as fly ash or the like.

The masonry structure forming the fifth aspect of the present invention may incorporate any desirable mortar. It is preferred that the mortar comprises cement, lime and/or sand.

In a preferred embodiment of the fifth aspect of the present invention the mortar comprises cement, lime and sand, in any suitable ratio, such as 1 part cement: 0.5 parts lime: 4.5 parts sand, as in class II mortar. The mortar preferably exhibits a 7-day compressive strength of 5.1 MPa, a 14-day compressive strength of 9.1 MPa, and/or a 28-day compressive strength of 10.8 MPa.

The masonry structure according to the fifth aspect of the present invention preferably exhibits a 60-day creep coefficient of around 2.1, and/or exhibits shrinkage over time, for example over a time period of around 10 to 60 days.

The manufacturing process of Bitublock preferably involves three fundamental processes; mix; compact; and cure. It has been shown previously that one of the main factors affecting the properties of Bitublock is the level of compaction; it is assumed that bonding of the aggregate and the binder is achieved through encapsulation rather than chemical interaction, as is the case with cementitious bound or even clay bound units. However, although this assumption is currently being investigated qualitatively, it was decided to confirm the presence of any quantitative effects. in some clay masonry, an enlarged free expansion has been measured due to cryptoflorescence. This results from the chemical interaction of the brick and the cement mortar and can cause expansions far greater than would be expected from a consideration of the irreversible expansion of individual unbonded clay bricks. Previously, it has been proposed that any enlarged expansion or chemical interaction between the unit and the binder can be identified by the model developed by Brooks (Brooks 1990). Masonry composed of Bitublock units and cement mortar were therefore constructed and time dependent movements (creep and moisture' movement strains) were obtained. Composite modelling of the long-term deformations of the masonry was performed to investigate whether the encapsulation of the recycled material by the bitumen binder does eliminate any chemical interaction with the mortar.

The theory and derivation of the models has been presented elsewhere (Brooks 1990) arid hence only the prediction equations are presented here.

Modulus of Elasticity (E) of Bitublock wall 1 b.C1 A 1 m(C+1) 1 I 1+ (1) H LEby.Ab+Em.Amj H Em where: E= effective modulus of Bitublock wall; b= height of block unit; C= number of courses (layer); H= height of wall; Eby= elastic modulus of block unit; Ab= cross sectional area of block unit; Em = elastic modulus of mortar; Am cross section area of vertical mortar joints; m= thickness of mortar bed joints; A = cross-sectional area of masonry.

The dimensions of the Bitublock unit and wall were as follows: b = 65mm; A,, 435x100mm; Ab = lOOxIOOmm; Am 33500mm2; m= 10mm. For the 7-course wall investigated, as shown in Figure 9, equation (1) becomes: ----=0.8426[ 1 1�0.1481 (2) L0.229Eby + 0.770Em] Em Creep To model creep behaviour, equation (4) is used however the initial modulus of the individual brick and mortar prism is replaced by an effective modulus (E') to allow for creep. Thus for a unit stress: Creep for wall: -4------.--(3) where E and are the effective and initial elastic modulus of wall Vertical shrinkage The general expression of the vertical shrinkage (S) at any time is b.C m.(C+1) b.C SmSb y y y S =-.S,, + .S +- H H m H Ab.EbY 1+---------. Am.Em

where Sby vertical shrinkage of block unit and Sm shrinkage of mortar. For the Bitublock wall investigated, the third term of the equation is small, so that equation (8) becomes: Swy = 0.8426 Sby + 0.1418 Sm (5) The experiments described below are intended to compare the compressive strength of the Bitublock units compacted at pressures between 1 and 4 MPa with concrete block units commonly used in the UK: 3.5 -10 MPa (Sear 2005 and British Standard-BS 6073 1981), (it has been found that the compressive strength property is a good indicator of overall block performance) and report the other physical and mechanical properties of the Bitublock units. Moreover, an investigation of the creep and moisture' movement strain of masonry structures, i.e. walls, constructed from the Bitublock units is described.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying figures, in which: Figure 1 is a graph showing Bitublock grading used in comparison to a hot rolled asphalt (HRA) as specified in the British Standard 594 (BS594), an example case.schematic perspective view of an upper portion of components of an embodiment of the present invention; Figure 2 is a graph showing Bitumen content vs. density; Figure 3 is a graph showing Bitumen content vs. porosity; Figure 4 is a graph showing Bitumen content vs. compressive strength; Figure 5 is a graph showing creep test results of Bitublock units, at 1 and 2 MIPa compaction levels; Figure 6 is a graph showing expansion of Bitublock units; Figure 7 is a photograph showing the prism creep rig; Figure 8 is a graph showing time-dependent movements of mortar prisms; Figure 9 is a photograph showing the loaded and control wall; Figure 10 is a schematic presentation of the vertical and horizontal strain reading; Figure 11 is a photograph showing the Demec gauges and strain reading; Figure 12 is a photograph showing the steel tie-bar load cells and the data logger; Figure 13 is a graph showing measured / predicted vertical shrinkage of control walls; and Figure 14 is a graph showing measured / predicted creep of walls.

EXPERIMENTAL

Performance Criteria The target performance for the Bitublock unit is as follows: -Compressive strength: �= 3.5 MPa at room temperature. This is in line with the compressive strength of concrete blocks commonly found in the UK: 3.5 -10 MPa (Sear 2005 and British Standard-BS 6073 1981).

-Initial rate of suction (IRS) values shall be equal to IRS values of clay brick found in the UK (0.25-2.0 kg/m2/min). The IRS is a parameter that can provide an indication of the effect of the unit on the cement mortar. Units with high IRS require very plastic mortar (high water/cement ratio), while units with lower IRS need stiffer mortar (BS3921 1985 and Vekey 2001).

-Possess specific creep (static creep strain per unit stress in MPa) of �= 100 microstrain, tested at 20 °C. This target is in line with the specific creep level of concrete blocks currently used in the UK (approximately 100 microstrain). The level of stress of I MPa shall be used for the creep test as this is considered representative in masonry experiments (Tapsir 1985 and Forth et al. 2006).

Materials Bitumen Type and Content In principal, all types of bitumen (hardlpenetration grade or bitumen emulsion) can be used as a binder. However, it is preferable to use a softer grade bitumen as this requires a lower handling temperature. Also, as the samples must be cured in order to improve their resistance to long-term deformation, the use of a harder grade bitumen would not provide a significant improvement to the end product. The type of bitumen used for this investigation was 50 penetration grade bitumen (also referred to as 40/60 pen.) with a specific gravity of 1.03 and a softening point of 47 °C. A range of bitumen contents between 5 and 6.5% was considered.

Materials Density Water (gr/cm3) Absorption (%) Coarse aggregates (CA) Steel slag 3.39 1.9 Crushedglass 2.51 <0.5 Fine Aggregates (FA) Crushed glass 2.51 <1 Filler Fly ash Ferrybridge 2.16 -Table 1. The properties of the aggregate materials.

Aggregate type For this investigation steel slag, crushed glass and fly ash aggregates have been used.

Table 1 provides details of the aggregates used in this investigation.

In order to reduce the amount of bitumen needed, (and hence enhance the economics of the mix) and yet still ensure satisfactory bitumen coating, the incorporation of waste aggregates with low absorption properties has been considered for this investigation.

Aggregate grading The choice of aggregate grading is largely affected by the performance criteria specified above. It has been found that a gap graded distribution of aggregates consisting of about % coarse aggregates (max nominal size of 14 mm; minimum retained 2.36 mm) and % fines (50 % fine aggregates (2.36-0.075mm) and 10 % filler (passing 0.075 mm) was preferable. Table 2 provides details of the aggregate and their proportions.

Figure 1 illustrates the aggregate distribution and compares it to British Standard 594, (BS594 2003). It can be seen that the fine fraction follows the lower limit of a hot rolled asphalt (HRA) grading. However, the coarser fraction (retained 2.36mm) tends towards the upper limit.

Mix Name Coarse aggregates: Fine Agg.: Filler: (40 %) 2.36-0.075mm <75j.tm 25% 15% (50%) (10%) (14-10) and (5-2.36) (l0-5)mm mm SSCF200/24 steel slag crushed glass crushed glass fly ash Table 2. Type of mix and aggregate materials used Bitublock unit optimisation The manufacture of Bitublock has been reported previously (Forth et a!. 2006). Briefly, to facilitate mixing, the aggregate materials and the 50 pen bitumen were pre-heated at 160-180°C (Withoeak 1991) for 3 hours. The loose mix was then placed in a mould and compacted. Following compaction, the Bitublock samples were cured in an oven (for this investigation the samples were cured at 200°C for 24 hours). The performance of Bitublock is influenced by porosity and the heat curing regime. A lower porosity (higher compaction) gives improved aggregate interlock which increases the potential compressive strength. However, more efficient heat curing (higher porosity -greater depth of bitumen oxidation / hardening) improves the long-term stability of Bitublock (i.e. reduces the creep potential). In this investigation, the curing regime was fixed and the compaction level and bitumen content were varied. Figures 2 to 4 illustrate the optimisation of bitumen content and compaction level.

Referring to the aggregate grading shown in Figure 1, the minimum bitumen content for road bituminous mixtures recommended by BS594 is 6.5 % by weight of total mixture; this is to ensure adequate coating and durability. With this in mind, the bitumen content was optimised taking the figure of 6.5% as a maximum.

From Figures 2 and 3 it can be seen that a decrease in bitumen content from 6.5% to 5%, corresponds to a decrease in density and an increase in porosity. This is because the mixture becomes less workable at lower bitumen contents.

A reduction in compaction level corresponds to a decrease in density and an increase in porosity. The compressive strength trends shown in Figure 4 are in line with the trend identified for density. However, for units compacted at 2MPa there is little improvement in compressive strength beyond 6% bitumen content. Further increases in bitumen content (higher than 6.5 %) may enhance the density and hence the compressive strength. However, by observing the satisfactory degree of coating of the aggregates; the surface texture of the units and the stability of the samples during handling, together with the insignificant improvement in compressive strength of samples with over 6% bitumen content compacted at 2MPa, it was decided not to optimise the bitumen content further. For the remainder of this investigation the bitumen content was fixed at 6 % and the compaction level at 2 MPa. The compressive strength of these units still exceeded the compressive strength of concrete blocks commonly used in the UK (3.5 -10 MPa). Also, a 0.5 % reduction in the bitumen content and a slightly higher porosity is expected to improve the long-term stability of the unit (this is considered in the next section). The initial rate of suction (IRS) of these optimised units (6 % bitumen content; 2MPa compaction level) was 0.35 kg/m2.min; the 24-hr water absorption value was 5.5%.

Long-term stability of the Bitublock units Prior to monitoring the time-dependent properties of the Bitublock units, the samples were stored in a controlled environment of 62% � 1% relative humidity and 21.5°C � 0.5°C. The samples were between 3 and 4 weeks old when they were tested. At this age, the volume stability of the unloaded samples was found to be very stable (i.e. the samples did not exhibit any expansion / shrinkage).

Figure 5 illustrates the total strain and creep of the Bitublock samples compacted at I and 2 MPa. The samples were loaded in a controlled environment using a static dead-weight lever arm machine (mechanical advantage of 4) providing a stress of I MPa.

Strain measurement was performed using both a 50mm Demec gauge and electrical resistance strain (e.r.s.) gauges.

Figure 5 also illustrates the elastic strain of the samples. A summary of the elastic and time-dependent properties of the samples is shown in Table 3. Although the creep of the units compacted at both I and 2MPa were acceptable (in terms of their comparison with concrete blocks), the unit compacted at 2MPa was chosen for construction in the Bitublock walls.

Mix Name Total Elastic Creep Elastic Strain () Strain (.t) Strain (jt) Modulus 2 (GPa) 1 MPa compaction level SSCF200/24 321.75 232.65 89.1 4.3 2 MPa compaction level SSCF200/24 79.2 34.65 44.55 28.9 creep strain = total strain -elastic strain -shrinkage or expansion.

2 elastic modulus = (1 MPa I elastic strain) Table 3 Creep performance of the samples As mentioned above, the unloaded volume stability of the Bitublock units was obtained from units which were 3 to 4 weeks old (corresponding with the age of the creep samples). Two samples were also later manufactured and monitored from an age of I day (after they had cooled to room temperature). The results of these tests can be seen in Figure 6.

These results are interesting as they illustrate a behaviour similar to kiln fresh' clay bricks. This early age behaviour of Bitublock is currently being examined to see whether it is a consequence of water absorption / adsorption. Figure 6 illustrates how stable the Bitublock units are after 15 to 20 days.

Mortar Details A class II; 1: Y2: 4 Y2, cement: lime: sand mortar was used throughout this investigation with 7, 14, and 28 day compressive strengths of 5.1, 9.1 and 1O.8MPa, respectively. The time-dependent properties of the mortar were obtained from 75x75x200mm prisms as described previously (Brooks and Abdullah 1988), (also see Figure 7 for details of the creep rigs). Readings were taken from an age of 7 days. Prior to this the prisms were cured under plastic.

Figure 8 illustrates the creep and shrinkage of the class II mortar used in this investigation. The behaviour is similar to mortar data measured in other similar investigations. The prisms in this investigation were unsealed. Therefore, for the composite modelling exercise later, this data will have to be modified to take account of the difference in volume / surface area (v/s) ratio between the mortar prisms and the mortar in the Bitublock walls (to compensate for the different drying paths).

Construction and testing of Bitublock walls The walls were constructed in a controlled environment, with temperature of: 21.5 � 0.5 °C and relative humidity (R.H) of 62�1%. The size of the Bitublock units was 1 OOx I OOx65mm; the units were approximately 30 days old. Four sets of walls were constructed. Each wall was 4 units wide by seven courses high (Figure 9). The walls were constructed with a class II mortar with joints of between 5 and 8mm thick.

Immediately after construction the walls were covered with plastic bags and cured for 7 days prior to being exposed to drying in the controlled environment.

Each set of two walls consisted of a loaded wall (to isolate creep) and a corresponding control wall (to obtain expansion / shrinkage deformations). On each side of the walls, vertical strain readings were taken at 4 locations and horizontal reading at three positions (Figure 10).

The strain readings were initially taken twice a day. After two weeks, the strains were recorded once a day and after one month, strains were recorded twice a week. Vertical strain readings were taken using a 150mm Demec gauge; horizontal strain readings were taken using a 200mm Demec gauge (Figure 11). Only the vertical strain data have been reported here.

The walls were loaded at an age of 7 days; a stress of I MPa was applied to the loaded walls. This stress was monitored and constantly maintained throughout the duration of the tests using 4 calibrated steel tie-rod load cells. (Any load adjustment required was possible by tightening / loosening the nuts on the tie-bars (Figure 12).) For practical reasons, the tests were only performed for 60 days. This was shorter than was envisaged however the data collected was considered sufficient for the purposes of this investigation.

Modulus of Elasticity The average modulus of elasticity of the Bitublock walls was 4.3GPa. The elastic moduli of the unbonded Bitublock unit and the mortar prism samples were 28.9 and 2.OGPa, respectively. (The modulus of the wall is clearly influenced by the modulus of the mortar.) The measured elastic modulus compares well with the modulus predicted using British Standard BS5628-2. For a unit strength of 14.2MPaand a class II mortar, the code predicts a modulus of4.61GPa.

It is normal practice to apply the load to the walls within 15 minutes. According to Neville 1983, this limits the incorporation of creep within the strain measured on application of the load to acceptable levels. However, in this investigation it was reported that the time for application of the load was between 15 and 30 minutes. The elastic strain will therefore contain some creep and the elastic modulus will therefore be lower than expected. This is confirmed by the prediction of elastic modulus using the composite model (equation (2)). An elastic modulus of 5.64GPa is predicted which is higher than the measured modulus.

Time-dependent behaviour Figures 13 and 14 illustrate the time-dependent behaviour of the Bitublock walls. It can be seen that the moisture movement behaviour of the Bitublock control walls is one of shrinkage (Figure 13). The Bitublock units are stable and so the movement of the wall will be controlled by the mortar which shrinks. This trend of overall shrinkage of the masonry agrees with previous findings of research performed on clay brick masonry, although this could not necessarily have been predicted and, indeed, BS5628-3 1995 recommends that all fired clay masonry expands.

Using the unbonded unit and mortar prism data (adjusted for v/s ratio differences) in the composite model expression (equation (5)) yields a slight over-prediction of shrinkage at early ages (Figure 13). However, at later ages the model under estimates the shrinkage of the walls (although the error is less than 20%, which is considered acceptable). Previously it has been shown that the composite model tends to over-predict the shrinkage of clay masonry. This is because the model does not entirely account for the interaction between the mortar and the unit in the masonry resulting from the water absorption properties of the unit. The Bitublock units in this investigation have very low water absorption properties and this interaction would be expected to have less effect. More importantly, the absence of any enlarged expansion' (the brickwork / brick expansion ratio is less than unity (Forth and Brooks 2000)) and the accuracy of the prediction indicates there is no chemical interaction between the elements of the masonry and that cryptoflorescence does not appear to be present.

The creep-time characteristics of the Bitublock wall can also be seen in Figure 14. The pattern of movement is similar to that seen for the mortar prisms and the unbonded Bitublock unit in Figures 8 and 5, respectively. The level of creep is also similar to that previously measured in concrete block masonry (Forth et al. 1996). Overall the composite model under-estimates the creep of the Bitublock masonry (approximately 25%) however beyond 10 days the measured and predicted creep is very similar.

The 60-day creep coefficient obtained for the Bitublock masonry of this investigation is 2.1. This value is within the range of design values suggested by BS5628-2 1995 (1.5 and 3.0 for clay and concrete block masonry, respectively). However, an exact comparison cannot be drawn as the code recommendations are ultimate values.

The investigation described above provides further proof of the concept of Bitublock and that the physical and mechanical properties of Bitublock units are at least equivalent to concrete block masonry units used in the UK.

This is the first time the elastic and time-dependent properties of Bitublock masonry have been investigated. For the experimental conditions of this investigation, composite modeling using un-bonded unit and mortar deformations gives reasonable estimates of elastic modulus, shrinkage and creep of Bitublock masonry. The use of composite modeling has helped to confirm the apparent absence of any chemical interaction between the mortar and the unit in terms of what effect this might have on the long-term behaviour of Bitublock masonry. The manufacture of Bitublock is an encapsulation process (its properties are not dependent on chemical binding). The results of this investigation help to confirm that the recycled material used in Bitublock is adequately encapsulated by the bitumen.

Overall, Bitublock is compliant with the design suggestions of the relevant British Standards for masonry.

REFERENCES

British Standard (BS) 6073-1, "Precast concrete masonry units", 1981.

British Standard (BS) 3921, "Specification for clay bricks", 1985.

British Standard (BS) 5628-2, "Structural use of reinforced and pre-stressed masonry", 1995.

British Standard (BS) 5628-3, "Materials and components, design and workmanship", 1995.

British Standard (BS) 594-1, "Hot rolled asphalt for roads and other paved areas-Part 1: Specification for constituent materials and asphalt mixtures", 2005.

Brooks, J.J., Abdullah, C.S., "Composite model prediction of the geometry effect on creep and shrinkage of clay brickwork", Proceedings 0f8IBMAC, Ed. J. W. de Courcy, London, Elsevier, Applied Science, 1988.

Brooks, J. J., "Composite modelling of masonry deformation", Materials and Structures, RILEM Proceedings Vol. 23, 1990, pp. 241-51.

Brooks, J.J., Abdullah, C.S., "Composite Modelling of the Geometry Influence on Creep and Shrinkage of Calcium Silicate Brickwork", British Masonry Society Proceedings, No.4, 1990.

Communities and Local Government, Planning, Building and the Environment -Zero carbon Homes 2006 http://www.communities.gov. uklplanningandbuildjng/theenvjronmentJzerocarbonhomes/ Environment Agency -Landfill Capacity 2005; http://www.environmentagency.gov.uk/subj ects/waste/l 031954/315439/1720716/17469 94/?version=1 &lang=_e European Union Thematic Strategy on the prevention and recycling of waste, December 2005, http://ec.europa.eu/environment/waste/strategy.htm Forth, J. P. and Brooks, J. J., "Influence of mortar type on the long-term deformation of single leaf clay brick masonry, Proceedings of the British Masonry Society, 4th IMC, 1995, pp 157-161.

Forth, J. P. and Brooks, J. J., "Cryptoflorescence and its role in the moisture expansion of clay brick masonry", Masonry International Conference, Autumn 2000, pp. 55-60.

Forth, J.P., Zoorob, S.E., Thanaya, I.N.A., "Development of bitumen-bound waste aggregate building blocks Proceedings of the Institution of Civil Engineers, Construction Materials, Volume 159, Issuel, February 2006, pp 23-32, ISSN 1747- 650X, Thomas Telford-London.

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Claims

CLAIMS1. A method for producing a masonry unit, the method comprising forming a mixture containing a bituminous binder and a graded aggregate containing a coarse aggregate fraction, compacting the mixture at a compaction level of up to around 7 MPa, and at least partially curing the compacted mixture.
2. A method according to claim 1, wherein said compaction level is around 0.5 to 5 MPa.
3. A method according to claim 1, wherein said compaction level is around 1 to 4 MPa.
4. A method according to claim 1, wherein said compaction level is around 2 MPa.
5. A method according to any preceding claim, wherein the mixture comprises up to around 10 wt % bituminous binder.
6. A method according to any one of claims I to 4, wherein the mixture comprises around 6 wt % bituminous binder.
7. A method according to any preceding claim, wherein the bituminous binder comprises 50 penetration grade bitumen.
8. A method according to any preceding claim, wherein the graded aggregate contains around 20 to 60 wt % of the coarse aggregate fraction.
9. A method according to any one of claims 1 to 7, wherein the graded aggregate contains around 40 wt % of the coarse aggregate fraction.
10. A method according to any preceding claim, wherein said mixture is produced by heating and mixing the graded aggregate and the bituminous binder.
11. A method according to claim 10, wherein at least one of the graded aggregate and the bituminous binder is heated to a temperature of up to around 200 °C.
12. A method according to claim 10 or 11, wherein said at least one of the graded aggregate and bituminous binder is heated for a time period of up to around 5 hours.
13. A method according to any preceding claim, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture to a temperature of up to around 250 °C.
14. A method according to any one of claims 1 to 12, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture to a temperature of around 80 to 240 C.
15. A method according to any one of claims 1 to 12, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture to a temperature of around 200 °C.
16. A method according to any preceding claim, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture for a time period of up to around 72 hours.
17. A method according to any one of claims I to 15, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture for a time period of around 24 hours.
18. A method for producing a masonry unit, the method comprising forming a mixture containing a graded aggregate and around 6 wt % of a bituminous binder, compacting the mixture, and at least partially curing the compacted mixture.
19. A method according to claim 18, wherein the graded aggregate contains a coarse aggregate fraction.
20. A method according to claim 19, wherein the graded aggregate contains around wt % of the coarse aggregate fraction.
21. A method according to claim 18, 19 or 20, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture to a temperature of up to around 250 °C.
22. A method according to claim 18, 19 or 20, wherein said at least partial curing of the compacted mixture is effected by heating the compacted mixture to a temperature of around 200 °C.
23. A method for producing a masonry unit, the method comprising forming a mixture containing a graded aggregate and a bituminous binder, compacting the mixture, and at least partially curing the compacted mixture by heating the compacted mixture to a temperature of around 200 °C.
24. A method according to claim 23, wherein the graded aggregate contains a coarse aggregate fraction.
25. A method according to claim 24, wherein the graded aggregate contains around wt % of the coarse aggregate fraction.
26. A method according to claim 23, 24 or 25, wherein the mixture comprises up to around 10 wt % bituminous binder.
27. A method according to claim 23, 24 or 25, wherein the mixture comprises around 6 wt % bituminous binder.
28. A method of producing a masonry unit substantially as hereinbefore described.
29. A masonry unit produced according to a method defined in any preceding claim.
30. A masonry unit substantially as hereinbefore described.
31. A masonry structure comprising a plurality of masonry units and a mortar, at least one of said masonry units comprising a graded aggregate and a bituminous binder.
32. A masonry structure according to claim 31, wherein the at least one of said masonry units comprises up to around 10 wt % bituminous binder.
33. A masonry structure according to claim 31, wherein the at least one of said masonry units comprises around I to 8 wt % bituminous binder.
34. A masonry structure according to claim 31, wherein the at least one of said masonry units comprises around 6 wt % bituminous binder.
35. A masonry structure according to any one of claims 31 to 34, wherein said graded aggregate comprises a coarse aggregate.
36. A masonry structure according to claim 35, wherein the graded aggregate contains around 40 wt % of the coarse aggregate.
37. A masonry structure according to any one of claims 31 to 36, wherein the graded aggregate comprises around 80 to 40 wt % of a fine aggregate.
38. A masonry structure according to any one of claims 31 to 36, wherein the graded aggregate comprises around 50 wt % of a fine aggregate.
39. A masonry structure according to any one of claims 31 to 38, wherein the graded aggregate comprises up to around 10 wt % of a filler material.
40. A masonry structure according to any one of claims 31 to 39, wherein the mortar comprises cement, lime andior sand.
41. A masonry structure according to any one of claims 31 to 40, wherein the masonry structure exhibits a 60-day creep coefficient of around 2.1.
42. A masonry structure according to any one of claims 31 to 41, wherein the masonry structure exhibits shrinkage over time.
43. A masonry structure substantially as hereinbefore described.