| الملخص | This study was carried out to assess the possible use of Tellol Al–Kind clay deposit in Naenava city for the production of lightweight aggregates. Two methods of heat treatment were tried. Iso-thermal firing was conducted at 1180- 1200˚ C range using different socking time for aggregates made from clay only. Whilest, rapid (flush) firing at 1200˚C was tried for clay mixed with different types and amounts of additives (dolomite, waste engine oil, and straw).The iso–thermal tests reveals that, bloating can occurs only at 1180˚C for 45 minutes holding time. The aggregates obtained, have a sp.gr., 1.38 with 0.8 % water absorption. In rapid firing, it was found that, the bloating of the clay can significantly improved by the addition of dolomite. The results obtained indicated that, aggregates of 1.35 sp.gr with about 1% water absorption can be produced from aggregates made of clay + 5 wt % dolomite. The firing time being about 5 minutes. These results encourage the use of Tellol Al- Kind for the production of lightweight aggregates. Obviously, from economic stand point rapid firing is mostly recommended. This lightweight aggregate can be used in insulation fill in constructions.
Keyword: Bloating, Montmorillonite, Heat treatment, Clay expansion, lightweight aggregates
Introduction
Lightweight aggregates (LWAs) are defined as natural or artificial materials which are granular and distinctly more porous than sand, gravel, or ground rocks and posses lightweight characters (have considerably low apparent specific gravity). They can originate from different natural resources such as volcanic rocks (pumice and tuffs), sedimentary and metamorphic rocks (claystones, slates and shale) or from waste materials and industrial by products (Fakhfakh et al., 2007 and Corrochano et al., 2009). LWAs, however, may range from extremely light in weight (unit weight not exceeding 0.8 g/cm3, with compressing strength nearly exceeding 70 kg/cm2) employed chiefly for insulators and non-structural concrete all the way to that used for structural concrete. For this,the minimum compressive strength is of about 176 kg/cm2, and possessing unit weight not exceeding 1.8 g/cm3 is required(ACI Committee 1999).
MATERIALS AND METHOD
Clay sample from Tellol Al-Kind deposit was used as the starting materials for the preparation of lightweight aggregates.Additives such as dolomite, straw and waste engine oil were used as a gas forming materials. Mineralogical and chemical composition of the clay and dolomite are shown in Table (1).
The raw clay was prepared to pass 150 micron, where as dolomite was made to pass 75 micron by crushing and grinding. The clay powder with or without additives (dolomite, oil, and straw) was mixed with water and kneaded to be sufficiently plastic. The mix was then extruded to form a cylindrical bars from which granules in the range of (-9.5 mm to +4.7mm) were prepared .The granules were dried at room temperature and then in oven for 24 hr. Additional heat treatment was made at 600˚C for 15 min.. Next the aggregates were fired in a muffle furnace at different temperature and time. The clay aggregates (granules) were treated by an isothermal firing mode, were heated from ambient temperature to the pre-determined firing temperature (1170-1200)˚C using different socking time (10-45)min. the rate of heating was (10 ˚C/min). On the other hand, rapid firing was used for the treatment of the aggregates made from clay with additives (aggregates made from clay only were tested also). The dried aggregates were directly introduced into a muffle furnace pre-heated at (1200˚C) for (5min) holding time. In both methods of firing the aggregates were removed from the furnace, cooled and then used for bulk density and water absorption measurements. The prepared aggregates, however, were made of six groups according to the type of additives as shown in Table (2).Mix design of proportion 1: 2: 2 (cement: sand: gravel)was used as concrete mixes, this mix was prepared by weight proportions for normal concrete, and by volume for lightweight concrete . Subsequently the specimens were carefully removed from the molds after 24 hr, labeled, immersed in tap water, and kept for curing for 28 days (age of testing of compressive strength).
RESULTS AND DISCUSSION
The mineralogical composition of Tellol AL-Kind clay and dolomite are summarized in Table (1), this indicated that, montmorillonite, palygorskite and kaolinite are the predominant clay minerals present. Other predominant minerals are calcite, , quartz and Feldspar. The chemical analysis, however, showed that the clay contain high amount of CaO (13.34%), obviously it is related to calcite (CaCO3). Na2O and K2O contained are mainly attributed to the presence of feldspar.
In general, the temperature range used for commercial bloating of clay usually between (1050˚C-1200˚C). Table (3) shows the results of the bloatability tests of Tellol Alkind clay which were carried out at (1180˚C-1200˚C) for different socking time. From these results it can be noted that, bloating of the clay was occurred only at 1180˚C for 45 minutes residence time. The specific gravity of the produced aggregates was of about (1.38) which is well below that (1.96) of the starting materials, with water absorption value of (0.8%), rapid (flush) firing at 1200˚C of the clay,indicated that a good bloat occurred, and a sp.gr of 1.47 can be attended.
The raw aggregates which were made from different proportion of the additives with the clay and fired for (3 and 5 minutes) at 1200˚C, are shown in Table (3). It is apparent that (clay + dolomite) materials can produce a good bloated aggregates with sp.gr from (1.49 to 1.35).Obviously the lower sp.gr value (1.35) is preferable and this obtained from the addition of (5wt% dolomite) to the clay. Beside (clay + dolomite) mix, (clay + 2wt% oil (CO2), (clay +1% and 2% straw (CS1 and CS2) reflects bloating action too. All others mixes shows poor bloating with higher specific gravity. However, comparing the properties of the aggregates obtained from the rapid firing (clay+5%wt dolomite) with that, obtained from the isothermal firing (using clay only), it can be noted that the aggregates produced from the isothermal firing for (45 min at 1180˚C) shows no significant differences from that, of the rapid firing. From the forging research it seems that, a number of factors may determine the bloating characteristics of clays. The type of minerals present in the clays and also their quantity.
However, the light weight aggregate prepared from clay+5% dolomite, and clay only by rapid firing was tested for lightweight concrete. The compressive strength after 28 days was determined and compared as shown in Table (4). It is obvious that the compressive strength of the light weight concrete in much lower than the normal concrete.. On the other hand concrete made from clay +5%dolomite lightweight aggregate, resulted with lower density (1.76 g\cm3) as well as low compressive strength.
CONCLUSION
- It is possible to produce lightweight aggregates considerably lighter (sp.gr. 1.38-1.35 range) than the conventional aggregates by:-a) iso-thermal firing of clay aggregates for (45min at 1180˚C), and -b) rapid firing for no more than (5min.) at 1200˚C of aggregates made of (clay + 5wt% dolomite).
- Economically, rapid firing method is most recommended for the production of lightweight aggregates from Tellol AL-Kind clay.
- The concrete made from the LWAs produced in this study has a compressive strength of about 172.6 kg/cm2 which fall mid way between low density and structural concrete this designated as fill concrete.
REFERENCES
ACI Committee, 1999. Guide for structural lightweight aggregate concrete. American concrete Institute. ACI 213R-87. P. 1-26.
Corrochano, B.C., Azcarate, J.A., Rodas. M., 2009. Production of lightweight aggregates from mining and industrial wastes. Journal of Environmental Management, vol. 9, p. 2801-2812.
Fakhfakh, E., Hajjaji, W. and Medhioub, M., 2007. Effects of sand addition on production of light weight aggregate from Tunisian smectite- rich clayey rocks. Applied clay sciences. Vol. 35, p. 228-237.
Table 1: The chemical and mineralogical composition of the clay and dolomite
Used in this work (in wt %).
Mineralogical Composition
Clay: Quartz, Calcite, Montmorillonite, Paplegorskite, Kaolinite, Rutile and Feldspar.
Dolomite: Mainly Dolomite with trace of Quartz
K2O
% Na2O
% L.O.I % SO3 % MgO % CaO % AL2O3 % Fe2O3 % SiO2 Sample Identify
1.55 0.17 18.26 0.09 4.05 13.34 12.18 5.69 43.83 C1ay
0.02 0.11 46.73 - 20.75 30.69 0.16 0.13 - Dolomite
Table 2: Groups of the aggregates mix. Preparation
Additives (in Wt %) Raw Clay% Sample
Material
Straw West Oil Dolomite
- - - 100 C Clay
- - 4 100 CD1 Clay + Dolomite
- - 5 100 CD2
- - 6 100 CD3
- 1 - 100 CO1 Clay + Oil
- 2 - 100 CO2
- 3 - 100 CO3
1 - - 100 CS1 Clay + Straw
2 - - 100 CS2
Raw material Sample Code Temp. Socking Time Density
g\cm3 (d) Wt. Abs. Bloating Appearances
Clay
+
Dolomite CD1
CD2
CD3 1200
=
= 3
=
= 1.424
1.367
1.49 1.1
0.934
0.392 good
V. good
good
CD1
CD2
CD3 =
=
= 5
=
= 1.470
1.350
1.4 0.4
0.996
1.73 good
=
=
Clay
+
Oil CO1
CO2
CO3 =
=
= 3
=
= 1.605
1.559
1.644 0.546
0.543
1.01 good
=
poor
CO3 = 5 2.035 0.584 poor
Clay
+
Straw CS1
CS2
CS3 =
=
= 3
=
= 1.56
1.512
1.60 1.2
1.49
1.54 good
=
poor
CS1
CS2
CS3 =
=
= 5
=
= 1.625
1.61
1.621 1.958
1.6
1.41 poor
=
=
Table 3: Physical properties of light weight aggregates, made from mixed materials
Table 4: Physical and mechanical properties of cube of concrete
Concrete Comp. st. kg/cm2 Density g/cm3 Water absorption%
Normal aggregate 270 2.16 3.7
Clay lightweight aggregate 172.6 1.98 5.9
Clay+5% dolomite lightweight aggregate 125.4 1.76 6.9 | en_US |
