STUDY OF USING THE CRUSHED CLAY BRICKS WITH NATURAL AGGREGATE AS UNBOUND SUBBASE PAVEMENT LAYER IN SEGREGATED FORM

: Construction and demolition of buildings and structures are producing excess or waste material which is including concrete, brick, steel, etc. Conservation and reuse of resources is a necessity in achieving sustainability across the globe, crushed brick could be safely added to crush rock blends in pavement sub-base applications with percent up to 25%. The experimental work was consisted of two groups of samples depending on percent volume of each material, each group samples have 6 different layering blends patterns prepared by spreading the pure materials in layers (segregated form) of Crushed Bricks Sand (CBS) and Natural Aggregate (NA), in addition to the two control samples and then experimentally tested to compare with the requirements of Iraqi specification for roads and bridges. The experimental work was consisted of Atterberg limits, sieve analysis, moisture-density relationship and California Bearing Ratio (CBR) tests. The results show that using of the crushed bricks as sand with natural aggregate as unbound subbase in segregated form is feasible and agreed with the Iraqi specification requirements because the CBR of CBS was improved when blended with the NA at all the patterns, the best pattern is that which containing three layers NA and two CBS (60% NA and 40% CBS by volume) and the NA was at the top, then CBS in alternated sequence that improves the CBR value to 1.6 times compared with NA control or 8 times of CBS control because the sporadic distribution reduces the effect of the low bearing material, in another words; collect the layers of the same material doesn't give best improvement. material and it's grade as fine aggregate). The next best pattern was the B2 because the top layer was NA which covered CBS. Although the pattern B1 consists of just 40% NA with 60 % CBS, it gave the same CBR % value of control NA sample because of reducing the displacement. And when compare it with CBS control blend, the CBR was improved to five times because the NA improve the CBS. This pattern test result satisfied the Iraqi requirements for subbase course depending on CBR (it is comply with type A). The CBR result of pattern B2 was 34.7% at 0.1 inch penetration and decreased at 0.2 inch to be 25% because the load had transmitted to the under layers which was lower bearing and high thickness of CBS allthough the top layer was the NA. This CBR value is larger than it's in pattern A6 in spite of increasing the CBS because the NA at top carry loads more than CBS. Although this pattern has the same percent of CBS like in pattern B1 but the CBR is less due to thickness layer of CBS (collected). Also, this CBR result is lower than the control NA sample due to presence and thickness of the low bearing CBS without spreads the NA between them. The CBR of B2 was improved for subbase layer to 3.7 times as compare it with CBS control sample.

Limited researchers had investigated on the possibility of using crushed clay bricks as aggregates in unbound subbase materials applications and they included that is feasible for using in subbase applications. Those researchers like: Zakaria and Rauf reported that, good quality brick aggregate in unbound condition has found to be satisfactory from strength consideration [6], Poon and Chan show that the replacement of recycled concrete aggregates by crushed clay brick further increased the optimum moisture content and decreased the maximum dry density and when the coarse crushed clay brick content increased. They show causes of that to the lower particle density and higher water absorption of crushed clay brick compared to those of recycled concrete aggregates, the subbase using crushed clay brick as the fine aggregate was less susceptible to moisture variations when compared to the subbase using recycled concrete aggregate as the fine aggregate. The use of crushed clay brick lowered the CBR value. A 4-day soaked period had a negligible influence on the CBR values of the recycled subbase [7], it was feasible to blend recycled concrete aggregate and crushed clay brick to produce a subbase with a soaked CBR value of at least 30%. Aatheesan  Arulrajah et al. (2013), evaluated the geotechnical and geo-environmental properties of five types of Construction and Demolition materials "Recycled Concrete Aggregate (RCA), Crushed Brick (CB), Waste Rock (WR), Reclaimed Asphalt Pavement (RAP) and Fine Recycled Glass (FRG)", they mentioned that "there is ability to improve the behavior of CB, RAP and FRG materials to enable their usage in pavement sub-bases by additives or mixed in blends with high quality aggregates", they find that limited work has been conducted on using crushed brick in geotechnical applications although there are several research works focusing on using CB in concrete mixture, concrete tiles and blocks [10].
The geotechnical properties of recycled CB had showed in some researches, like in Arulrajah et al., and from their study on CB from the recycling site (typically may consists of up to 30% other materials) with a maximum particle size of 20 mm, found that the fine content % (6.6), CBR % (123-138), compaction modified density (19.82 kn/m 3 ) with optimum moisture % (10.7), and Tri-axial test (CD) Cohesion (41.1kPa) [9]. And Mithaq Albeer Louis, et al., in their research worked on CB sand with the classification according to (USCS) was poorly graded sand (SP) and it is not plastic matter [11]. Also Arulrajah et al in their research, RCA, CB and WR in particular are found to also meet the physical and shear strength requirements for aggregates in pavement base/subbase applications [12]. In addition to Wijewardana et al had found the 100% recycled brick sample achieved a maximum dry density of 2020 kg/m3 and a CBR value of 113%. The blend of 50% crushed bricks and 50% gravel also satisfied the Atterberg limit dry density (1779 kg/m Other studies on CB with stabilizers were found to be viable for usage as pavement base/subbase construction materials. These studies like in Mithaq Albeer Louis, et al. when studied Blend the (RAP) with CB sand and stabilized with cement and/or lime, concluded that increasing bricks sand increase the compression strength objectives, this paper aims to use the (CBS) with easy method of construction to reduce waste material and conserve the natural one.

METHODOLOGY
The experimental work was consisted of two stages: First stage: the control blends samples were prepared to study the geotechnical properties of NA and the CBS each separately for a comparison later, figures (1 and 2) show the materials.
a. the natural aggregate sample. b. the molded sample.  Second stage: two groups of layering blends were prepared by spreading the the pure materials in layers, group (A) composed of (60% NA and 40% CBS by volume), group (B) (60% CBS and 40% NA by volume), different blends patterns of CBS with NA were prepared for each group as shown in table (1) and figure (3), then the samples was experimentally tested to compare with the requirement of Iraqi general specifications for roads and bridges.  To evaluate these types and to find the geotechnical properties, the tests below was achieved:

NATURAL AGGREGATE (NA):
The Natural Aggregate was the ordinary subbase material used in the middle and southern region of Iraq from Al-Najaf city quarries, graded as middle limits of subbase course type C as specified according to the Iraqi general specifications for roads and bridges (SCRB/ R6. 2007) [20] as shown in table (2). The Plastic and Liquid Limits are 18.5% and 23.7 % respectively, the Plasticity Index was 5.2 and the Maximum Dry Density M.D.D was 2.1 gm/cm3 with O.M.C 9.6%. The good gradation and presence of coarse aggregate lead to raise CBR, it was 45% at M.D.D. This result agreed with the Iraqi requirements for subbase materials. The high percent of fines with high plasticity make good bonds but the displacement increase when loading.

CRUSHED BRICKS SAND (CBS):
The crushed bricks sand brought from waste clay bricks then crushed to pass from sieve 9.5 mm. Figure (4) show the grain size. It's classification according to the Unified Soil Classification System as well graded sand (SW) and the Group Index (0). It's classification according to AASHTO method as A-3. Using of the crushed clay brick as the fine aggregate (sand) was low susceptible to moisture variations as shown in figure (5) that's also mentioned in Poon and Chan (2006) [7], it have the higher optimum moisture content due to the lower density and higher water absorption, this make the CBS feasible using in layer exposed to moisture like in subbase. The properties of CBS shown in table (3), CBR value was lower whan it's value in NA due to the gradation of CBS as sand (without coarse aggragte) and be not cohesive non-plastic material and became loose (without bonds) under moisture. The CBR value is high as compared with the origin materials of bricks (sand, clay, and silt), becuase its firing to 1000 0 C and dehydration and fusion process make it turns into a dense glass material to produce cohesion and hardness

FOR BLEND PATTERNS OF GROUP (A):
As shown in figure (6), the CBS bearing ratio was improved and the whole CBR results within the requirements of the Iraqi specifications for subbase type C. The CBR values were decreased from 72 % (at pattern A1) to 30% at pattern A6 Because of the collection of two or more adjacent layers of the same material, the characteristics of that substance will be shown. In contrast, when spreading the pure materials in alternated form layers consecutive NA then CBS , this will show the best results. So the best pattern was A1 which also because the NA at top which has the higher bearing ratio (due to presence of the coarse aggregate and fines bonding) covered the CBS layers (which was the loose and weak material), and the minimum thickness of the CBS made the load transmitted to the below NA layer which carried and supported, when compared bearing results of this pattern with the control blends, it is higher than the NA sample (by 1.6 times) and CBS (by 8 times), the sand works as leveling and reparation gradation the segregated particles from the previous spread layer also it is reducing the vertical displacement of the pattern due to its non-plasticity property in it's fines, and also CBS has higher CBR than ordinary soils fines with less susceptibility to moisture. The CBS at top layer reduced the bearing ratio due to it's charecteristics of not cohesive non-plastic material and loose (without bonds) and the less bearing without covering as shown in pattern A6, this CBR value was the least among all the patterns results not just due to presence of the low bearing (CBS) layer at top, but CBS didn't be between the NA layers to improve the NA layers by reducing the displacement, also lower than the control NA sample, this CBR was improved for subbase layer to 3.3 times as compared with the CBS control sample.

FOR BLEND PATTERNS OF GROUP (B):
As shown in figure (7), the CBS bearing ratio was improved and the whole CBR results within the requirements of the Iraqi specifications for subbase type C except samples B4 and B6 they are within the type D, the CBR values were less than those in group (A) due to the high percent of low bearing material (CBS) opposing NA in spite of reducing the vertical displacement. The best CBR result was 45% at pattern B1 then began to degrease to 26% because of collecting two layers or more of same material especially the NA (due to displacement). Also, the low values due to existence the CBS at top layer (loose, low bearing

CONCLUSIONS
Construction process of roads trending to use crushed bricks in pavement layers which is leading to study the feasibility of these materials, this paper studied using of the waste bricks crushed as sand in unbound layers and used with natural sub-base materials in segregated form to produce such study patterns, and its concluded that: 1. The density of CBS is low susceptible to moisture variations as shown in moisture-density relationship test figure (5), it have the higher optimum moisture content due to the lower density and higher water absorption that is make it feasible for using in layer exposed to moisture. 2. The CBR result of CBS alone was less than the limit of subbase course because it is not cohesive non-plastic material and became loose with moisture. 3. The use of crushed bricks as sand with natural aggregate as unbound subbase in segregated form is feasible and agreed with the Iraqi specification requirements because of the CBR of the CBS was improved when mixed with the NA at all the patterns. 4. The best blend is not just with increasing the material which has the high mechanical properties, but in pattern of its distribution within the depth and its position from the top layer. So, the best blend pattern is (A1) which have CBS spread between NA layers and NA at top. This had improved the CBR value compared with control sample of NA, and it gives supporting to the CBS layers. 5. Collecting layers of the same material together doesn't give best enhancement, and the sporadic distribution reduces the effect of low bearing material like in blend patterns. 6. As compared with the control sample of pure CBS, the CBR value is improved when blending 60% of the CBS with 40% of NA in patterns B1 and B2 to 5 and 3.7 times respectively, while in blending 40% of the CBS with 60% of NA, the CBR is improved to 8 times in blend pattern A1 (compared to the control sample of pure NA is improved about 1.6 times) and increased to 3.3 times in pattern A6.