Modulus of Elasticity and Impact Resistance of Chopped Worn- Out Tires Concrete

: This work investigates some properties of chopped worn-out tires concrete (Ch.W.T.conc.). It is a type of concrete characterized by the incorporating of Ch.W.T into the mixes as a partial replacement of volume of aggregate (sand and gravel of equal proportion). Three mixes of Ch.W.T conc. In addition to the reference mixes were selected, using Partial Replacement Ratio (PRR)of 30%, 40%, and 50%.The tests which were used in this study were: compressive strength, modulus of elasticity (static and dynamic), and impact resistance (low and high velocity). It was found that incorporating Ch.W.T in concrete effect on the properties of concrete, for example the percentage decreases in compressive strength were 41%, 46.7%, and 52.4% for concrete with 30, 40, and 50% Ch.W.T. PRR by volume of aggregate (50%


Abstract:
This work investigates some properties of chopped worn-out tires concrete (Ch.W.T.conc.). It is a type of concrete characterized by the incorporating of Ch.W.T into the mixes as a partial replacement of volume of aggregate (sand and gravel of equal proportion). Three mixes of Ch.W.T conc.
In addition to the reference mixes were selected, using Partial Replacement Ratio (PRR)of 30%, 40%, and 50%.The tests which were used in this study were: compressive strength, modulus of elasticity (static and dynamic), and impact resistance (low and high velocity). It was found that incorporating Ch.W.T in concrete effect on the properties of concrete, for example the percentage decreases in compressive strength were 41%, 46.7%, and 52.4% for concrete with 30, 40, and 50% Ch.W.T. PRR by volume of aggregate (50%      ٩٤ sand, 50% gravel) respectively. However, it gave good indicator to be utilized as a new construction material in many applications.

Introduction:
As a result of the wide progress that was achieved in the transport and the wide use of vehicles, this gave birth to various problems one of them is the environmental pollution. The combustion of large quantities of worn-out tires got accumulated, thus facing very serious problems of safe disposal, either by the wide land, which was needed to store or by the incineration of the large quantities [1]. Many researchers have endeavored to make use of enormous quantity of waste rubber tires and decrease environmental pollution resulting from them. The idea of using a material of chopped worn-out tires in construction material industry emerged as it enjoys several favorable characteristics such as high resistance to weather conditions, temperature and humidity, low water absorption and light weight in comparison with other materials that are usually used. It is also characterize by high-insulation capacity.
The use of chopped worn-out tires has several economic benefits such as:

Steel Reinforcement:
Deformed steel bars of 10mm diameter with yield strength of (350 MPa) were used throughout the present research.

Mixing Water:
Potable water was used for mixing and curing purposes.

Chopped Worn-Out tires:
A copped worn-out tire produced by Babel factory in Al-Najaf was used throughout the study, the maximum size of copped worn-out tires particles was 6.35 mm. The sieve analysis, the chemical composition and some properties of the copped worn-out tires are shown in Tables (4), (5) and (6) respectively.

Superplasticizer:
High Range Water Reducing Agent (HRWRA), which is known commercially as Melment L10, was used throughout this work as a (HRWRA).While maintaining equal workability to the reference mixture.
The technical description of this type is given in Table (7).    Steel molds were used throughout this work. The control specimens used in all tests were as follow: 1. For compressive strength, cubes of (100×100×100) mm are used.

Slab Specimens:
For impact strength test (low velocity), square slabs of (٥٠٠ ×500×50) mm with minimum reinforcement were used

Experimental Program:
The experimental program is planned to investigate the effect of using Ch.W.T. as a partial replacement of sand and gravel with admixtures (HRWRA) on the static and dynamic modulus of elasticity and impact resistance (low and high velocity) of Ch.W.T. concrete. Table (8) shows the details of reference and Ch.W.T. concrete mixes used throughout this work.

Mixing Procedure:
The mixing of concrete is important to obtain the required workability and homogeneity. A mechanical mixer of (0.1) m 3 capacity was used. The      ١٠٠ interior surface of the mixer was cleaned and moistened before placing the materials.
The raw materials such that gravel, sand, cement, and Ch.W.T were first mixed dry for about one minute concrete then water, or water content of admixture (HRWRA) was added to the mixer. After that mixing continued for about three minuets until the concrete becomes homogenous in consistency. The slump measured immediately after mixing, according to ASTM C-143-89 [5]

Casting Compaction and Curing:
The molds were lightly coated with mineral oil before use, according to ASTM C192-88 [6], concrete casting was carried out in different layer each layer of 50 mm. Each layer was compacted by using a vibrating table for (15-30) second until no air bubbles emerged from the surface of the concrete, and the concrete is level off smoothly to the top of the molds. Then the specimens were kept covered with polyethylene sheet in the laboratory for about (24±2) hrs.
After that the specimens remolded carefully, marked and immersed in water until the age of test. The specimens were tested at age of 7 and 28days for control specimens and (56 and 90) days for impact test.

Compressive Strength Test:
The compressive strength was determined according to B.S.1881.part 4, 1970 [7]. The average of compressive strength of three cubes was recorded for each testing age (7 and 28days).

Static and Dynamic Modulus of Elasticity ( Ec and Ed ):
The static modulus of elasticity was calculated by using the following formula and the average of three specimen results of age 90 days was adopted. The strain was measured using compressmeter according to ASTM C469-87a [8].
The dynamic modulus of elasticity was determined on the laboratory specimens subjected to longitudinal vibration on their natural frequency; according to B.S.1881.1970 [9].
The dynamic modulus of elasticity was estimated by using the following The average result of three specimens for each testing age 7,28, and 90days) was adopted

Impact Test:
Four (500×500×50) mm, slab specimens for each group were tested under low velocity impact load. The impact was calculated using (1020 gm) ball dropping freely from a height of 2.5 and 1.2 m. Two specimens were tested for each height at 90 days. The test rig used for low velocity impact test was illustrated in reference [10] After curing time of 90days, the specimens were white painted and placed in its position in the testing frame with the finished face up. The falling mass dropped repeatedly and the number of blows required to case first crack (usually      ١٠٢ observed) is recorded. In addition, the crack pattern and crack propagation were observed and recorded. The number of blows required for failure (no rebound) was also recorded.

Compressive strength:
The compressive strength was determined at age of (7,28) days for moist cured concrete specimens. The test results of compressive strength are summarized in Table (

Static and Dynamic Modulus of Elasticity (Ec and Ed):
The results of secant static modulus of elasticity Ec are shown in Table (11). The Ec values of Ch.W.T. concrete range between (32.8 to 26.7) GPa. for Ch.W.T. concrete with 30% ,40%, and 50% Ch.W.T by volume of aggregate respectively.
The test results of dynamic modulus of elasticity Ed are summarized in Table (11), from this Table it can be seen that the Ed decreases with increases of   The impact resistance results in terms of number of blows are shown in Table ( 12). The relationship between Ch.W.T. content and number of blows to first crack and failure (no rebound) are shown in Figs. (4) and (5) respectively.
The relationship between compressive strength and number of blows, which cause failure, is show in Fig. (6).
From test results, it can be seen that the presence of Ch.W.T. reduced that first crack impact resistance; this may be related to the fact that both aggregatematrix bond and the relative stiffness of aggregate and matrix have a role to play in impact resistance. So replacing the aggregate with Ch.W.T. reduces the first crack impact resistance of mixes, Fig(4). The percentage degreases of number of blows from 1.2 m height, which is caused first crack relative to reference concrete at 90 day were 20%, 36%, and 52% for Ch.W.T. concrete with 30%, 40%, and 50% Ch.W.T by volume of aggregate respectively. From 2.5 m height the percentage degreases of number of blows, which is caused first crack relative to reference concrete at 90 day were 40%, 60%, and 87% for Ch.W.T. concrete with 30%, 40%, and 50% Ch.W.T by volume of aggregate respectively.  However, specimens who appear to possess relatively low impact resistance to first cracking are not necessarily weak, in impact, and to seem to have high impact resistance to failure that is in agreement with previous work [2,11].
The effect of compressive strength on the impact resistance is plotted in Fig. (6), in general Green [12] found that the higher the static compressive strength of concrete the lower the energy absorbed per blow before cracking, but the impact strength of the concrete increases with its compressive strength (and there for age) at a progressively increasing rate.

Mode of Failure under Impact:
For all specimens the crack started at the center of bottom face of specimens and moved increasingly outward as the number of blows increased.
And for specimens failing with more than one major crack (more than two pieces), the crack pattern was that only one major crack appeared at the beginning of the test and with increasing that number of blows up to half of the ultimate number, the second crack appeared. The cracks continued increasing in width and length until the specimen is fractured into separated pieces.

Conclusions
Depending on the results of this investigation, the following conclusions can be drawn.