Utilization of Municipal Solid Waste Ash in Concrete by partial Replacement of Cement

The problem of solid waste is being emerged increasingly due to the increased quantity of solid waste as a result of population’s increase .From the point of view of environmental and energy concerns, it is preferable to reuse the organic and inorganic components of solid waste in order to minimize the cost. In this investigation, the possibility of using solid waste ash (SWA) as a partial replacement of cement and its effect on the mechanical properties of concrete was studied. Samples of municipal solid wastes were collected were burring and changed to ash. A total of 50 cubes, 15 small cubes, and 30 cylinders, as well as 5 prisms were prepared .Various properties of solid waste ash are added to the cement mistures with percent's of 5, 10, 15 and 20 percent by weight of solid waste ash. A concrete mix with a percent solid waste ash was used as reference. Pozzolanic activities of all mortars, and setting times of all pastes, and workability of all mixes were investigated .Compressive strength, splitting tensile strength, absorption, and drying shrinkage for reference for reference and solid waste concrete specimens were investigated at various ages. Results demonstrate that the pozzolanic activity was within ASTM requirements for the cases of 5% and 10% ash replacement. For 15 and 20 percent replacement this activity was only slightly less than the ASTM value. The 90-day compressive strength rose, in comparison with control specimens, with 5 percent replacement and was only slightly lower at 10 percent replacement. In splitting tensile strength was at least equal to reference specimens for all replacement ratios. The rise in these values, over the reference specimens, ranged between 0 to 21 percent for the case of 20 and 5 percent replacement, respectively.

Solid waste is the unwanted or useless solid materials generated from combined residential industrial and commercial activities in a given area. It may be categorized according to its origin (domestic, industrial, commercial, construction or institutional) according to its contents organic material, glass, metal, plastic paper, etc.); or according to hazard potential (toxic, non-toxin, flammable, radioactive and infectious, etc.). [1] Portland cement can be known as a power exhaustive material, then considerable effort is being made to find substitutes for partially replacing cement in concrete .For over 30 years the world had become increasingly involved in research aiming at power in the cement and concrete manufacturing. This was partly accomplished by encouraging the use of less energy intensive cementations materials for example, rice husk ash, fly ash, slags, condensed silica fume and pozzolans in concrete. [2] In this study solid, local SAW is used as a partial replacement of cement in concrete .Results of this research will provide important information about the pozzolanic activity of Iraqi SAW, the setting time, the compressive strength, the splitting strength, absorption, and drying shrinkage of concrete, the splitting tensile strength, absorption, and drying shrinkage of concrete, which contain Iraqi solid ash as a partial replacement of cement.
Samples of Municipal Solid Waste used throughout this work. The samples were collected from different points of beds. The first step in the preparation of solid waste to be used as a replacement of cement in concrete was its combustion with air .Dewatered solid samples were fired in an electric furnace with controlled temperature in order to establish the optimal burning temperature and time .The resulting ash was pulverized and only components that passed through the 150 µm sieve. The experimental program was planned to investigate the effect of using solid as a partial substitution of cement in concrete on the mechanical properties of concrete. The test variables include slump, compressive strength, splitting tensile strength, drying shrinkage, and absorption.
The physical analysis and chemical tests results of the cement use are given in table (1) and (2) Fly ash is the result of the burning of pulverized coal in thermal power plant life. It is removed by perfunctory collector or electrostatic precipitators as a fine particulate residue from the incineration gases before they are discharge to the environment [3].A combustion and properties of fly ash vary somewhat from one fly ash to another, depending on the specific coal being burned and on the details of the power station equipment and operating conditions [4] [5].
The generated solid waste ash from incinerator involves wide range of particles size; only the fraction 0-4 mm was used in the present work. The ash was dried before experiments. The content of major components (in form of oxides) is presented in Table. 4. The W/C or W/C+SOA ratio and pozzolanic activity index for various mixes are presented in table (5). Fig (1) shows the pozzolanic activity index in percentages. The SWA-Concrete mixes were designed with the same weight proportions except that a(5,10,15and 20)% of the cement weight was replaced by SWA. The (W/C+SWA) was the same as (W/C). [6,7] The molds were tightly coated with mineral oil before use, according to ASTM C192-88 [9].Concrete casting was carried out in two layers each layer of 50 mm. Each layer was compacted by using a vibrating table for (15-30) seconds until no air bubbles emerged from the surface of the concrete, and the concrete was leveled off smoothly to the top of the molds. Then the specimens were kept covered with polyethylene sheets in the laboratory for about (24+2) hour's .After that the specimens were remolded carefully, marked and immersed in water until the age of test. The ages of tests were 28, 60 and 90 day.

Index
Workability of all types of concrete was measured by slump test according to the procedure described in ASTM C143-89. [8] For compressive strength tests 100mmside concrete cubes were prepared according to B.S.1881. part 3 ,1983 [10].The compressive strength was determined using a(2000KN) capacity ELE digital testing machine of three cubes was recorded for each testing at age of 28,60 and 90 day.
The load was applied by using (2000kN) capacity ELE digital testing machine, continuously at a stress rate of 6 MPa per minute. Three cylinders was recorded for each testing time 28,60and 90 day of the average of splitting tensile strength.
The test was performed on 100mm cube in a accordance with B.S.1881:part 122:1989 [12].For each mix2cubes were taken from the curing basins and over dried to 105C 72hrs.Then they were wrapped securely with a polyethylene sheet and left in the laboratory to cool for 24 hrs.
After that they were weighted and then immersed in the water. After the immersion period of 30 minute, the cubes were removed and their surface were dried with a cloth and weighted again.
Prisms with dimension of (100*100*400) mm (weight *depth*length) were prepared and cast according to ASTM C192-88 [6]. Then they were demoded after 24 hour, and a stainless steel demec point was fixed on two parallel faces of specimens with a distance of 150mm between them in each face, after they were placed in a tank filled with tap water for 7days. After that they were stored in a dry place inside the laboratory at a temperature of about 28C and relative humidity of 26. The change length of specimen was measured by means of a dial gage of strain satisfy the requirement of ASTM C490-89 [14].The accuracy of the measuring device gage is 0.002 the shrinkage was measured at the ages of 7,14 and 28 day. [13] Initial and final setting times for reference and replaced cement paste samples are given in Table (6)and Figure 1.It is observed that the addition of solid waste ash due to replace of cement amount which effect on hydration process and consequently on setting time delays the setting times for the cement. The slump test results for all types of mixes are presented in table (7) and figure 2.generally, workabilityappears to improve with higher percentages of sludge ash in the concrete. This result shows on agreement to that which was found by previous researches. Thus, it seems at this stage, SWA concrete does not cause a workability problem because the SWA is soft material and not effective on workability.

Slump(mm)
The compressive strength values at 28,60 and 90-day ages for reference and various mixes with partial replacement of cement by solid waste ash are shown in table (8). The results indicate that sluge ash concrete with 5% replacement showed an increase in compressive strength at all ages of tests relative to its reference concrete, Figure 3.The compressive strength as the percentage of solid ash increased because of increasing the density of concrete matrix.    The results of the absorption test for various type of concrete specimens are given away in table (10) and Figure 5.As shown in table (10),water absorption for samples do not significant vary with the percentages of pulverized sludge ash used in concrete. Results show an agreement to those which were found by previous studies.  The results of the drying shrinkage test for all types of concrete specimens are shown in table (11) and figure 6.  1-Incinerating solid wastes is an efficient method compared with land filling to reduce the non-recyclable waste amount; the waste reduced by incineration is less than 30 % of original mass and the volume decrease is about 10 %. 2-The pozzolanic activity of the mortars decreases as the percentage of solid ash used increases . However , with 5% and 10% replacement of cement by solid ash. 3-The is aslight decrease in the initial and final setting times with an increase in the amount of replaced by solid west ash. 4-Solid waste ash concretes showed significant reduction in drying shrinkage at all age compared to reference concrete. 5-The concrete which has fly ash is an effective technique for the frost resistance. 6-The high percent fly ash without any accompanied loss of concrete properties possible only when the fly ash is treated by using vitrification method. where in such case there is arise additional costs suppressing the MSWI ashes utilization attractiveness for building industry. 7-Solid waste ash concretes exhibit a slight improvement in workability relative to their reference concrete.