e-ISSN: 2582-5208 International Research Journal of Modernization in Engineering Technology and Science Volume:03/Issue:02/February-2021
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ALKALI-SILICA REACTIVITY OF AGGREGATES IN HYDERABADJAMSHORO REGION Farhan Ahmed*1, Aneel Kumar*2, Samar Hussain Rizvi*3, Shabir Ahmed*4, Shahzeb*5 Department of civil engineering , Mehran UET Jamshoro, Sindh, Pakistan.
ABSTRACT Alkali-silica reaction is from one of the numerous chemical interactions that have a major impact on concrete’s durability. In ASR reaction, silicon content of aggregates possessing highly reactive silica reacts with alkali content present with in the cement. This Forms hygroscopic gel, which on absorbing water from it’s surrounding, expands and cause damage to the concrete structures. The aim of this research paper is to check the alkali silica reactivity of crushed gravels selected from quarries in the vicinity of Hyderabad and Jamshoro. In the study crushed gravel from two quarries in the vicinity of Hyderabad and Jamshoro were used. ASTM C 1260 research methodology was followed to check the Alkali silica reactivity of Crushed gravels. The result showed that expansion after 14 days of both the crushed gravel sources with OPC cement did not exceed 0.2 % limit, by ASTM C1260 research methodology (testing specimen dimension 25×25×285mm). Both crushed gravel sources were found of innocuous behavior and are safe against ASR.
I.
INTRODUCTION
Concrete is commonly used material in the construction sector. It is the major material used in constructing the largest and most prominent structures around the world including buildings, roads, hydraulic structures, power plants and many more other numerous structures. It is presumed to last for long-term periods because of its good durability characteristics. Nowadays, deterioration of concrete is a common problem seen in most of the structures around the world. Environment hazards like weathering actions, alkanity, freezing and thawing, carbonation, chemical attack and abrasion have reduced the durability of concrete. Not only the environment hazards influences the durability of concrete members but also the chemical interaction among the constituents of concrete ingredients has sufficiently effect on the durability and in general the lifespan of concrete (1). Variation in mineralogical and textural properties of the rock aggregate has considerable effect on durability of concrete. Excessive reactivity and harmful properties of rock aggregate cause expansion and cracking which ultimately results in loss of concrete strength and durability. Silica-alkali reaction (SAR) which is considered as cancer for concrete is the one of the effects of excess reactivity and deleterious properties of rock aggregate. ASR occurs in concrete due to reaction of silica that occur in concrete due to the disintegrations of the (Si – O) bonds in poorly crystallized aggregates with the OH ions present within the pore fluid of the cement paste. Silica- Alkali reaction (SAR) often results into the degradation of concrete structures (2). Silica -Alkali reaction (SAR) has become one of the most daunting threats in construction sector around the world. In order to prevent the damage in future, the liability of aggregates to occur Silica-alkali reaction (SAR) must be checked. Numerous test mythologies have been developed to check the liability of aggregate to occur SAR in concrete. Various laboratory tests have been established including ASTM C227, ASTM C295, ASTM C1293 and ASTM C1260 to access the SAR. ASTM C1260 and ASTM C 1293 being most popularly used laboratory methods due to the similarity in the results of the test and field performance history of aggregates in concrete at site (3).
II.
ALKALI-SILICA REACTION
Silica-Alkali reaction is a chemical interaction between the reactive silica that occurs in aggregates of certain forms with the alkali hydroxides present with in the concrete pore fluid. The alkalis present in concrete occur from certain amount of alkali content present within the cement and admixtures used in it. This reaction results in formation of gel which has characteristics to expand when it absorbs water from surroundings. Expansion of gel increases the internal stresses and results in the formation of cracks within the concrete structures. Whole process of alkali-silica reaction causes degradation of concrete and thus reduces the life of concrete structures. The severity of the deterioration depends on various reasons including the aggregate types and their chemical
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e-ISSN: 2582-5208 International Research Journal of Modernization in Engineering Technology and Science Volume:03/Issue:02/February-2021
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and physical properties, the intensity of gel formation, its amount contained by the concrete. Three factors are necessary for ASR to be occur in concrete. (4)
The pore solution should have alkali content; Reactive silica with in aggregates; Moisture content.
This paper reports the alkali-silica reaction of aggregates selected from different quarries in the vicinity of Hyderabad and Jamshoro, by using ASTM C 1260 research methodology.
III.
MATERIALS AND TEST METHODS
A. Material Used 1. Cement The cement used was belonging to Lucky Star Company, Pakistan and the type of cement was OPC. The properties of the cement which in this research work are shown in Table 1 Table-1: Cement used for making mortar prisms Cement
Properties
Specific gravity
3.12
Fineness
96%.
Normal consistency
0.34
Soundness
2.5mm
I.S time
74 min
F.S time
180 min
C.S at 28 days
51 Pa
2. Crushed gravels The Crushed aggregates from two quarries in the vicinity of Hyderabad and Jamshoro, Pakistan are selected. In this research following two aggregate sources will be checked for ASR by using ASTM C 1260 research methodology. Table-2: Crushed gravel sources Crushed Aggregates Quarry Source A
Near petaro in Jamshoro
B
Near Hyderabad- Jamshoro Toll Plaza
The liability of crushed gravels to occur ASR was tested according to ASTM C 1260 method. According to ASTM C1260 method, prisms of mortar having dimensions (25×25×285 mm) with gauge length 250mm are moulded and hardened. After 24 hours they are removed from mould and placed in water at 80°C and again after 24 hours they are removed and are placed in sodium hydroxide solution of molarity 1M for fourteen days at 80°C temperature and their linear expansion is noted periodically for fourteen days. This test method determines the degree of reactivity of aggregates from linear expansion limit as described below. After 16 days of casting, if Expansion of the specimens is < 0.10 %, then it shows that aggregates are of harmless nature. After 16 days of casting, if Expansion of the specimens is > 0.20 % , then it shows that aggregates are of harmful nature After 16 days of casting, if expansion of the specimens is between 0.10 and 0.20 %, then it is indicative of innocuous and deleterious both. For aggregates of such type, it is necessary to develop additional information. In such cases, comparator readings until 28 days are taken (5). www.irjmets.com
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The particle size of aggregates should be from 4.75 mm 150 m. Aggregates are crushed as per requirement shown in Table 3 and after that they are washed. Table-3: Grading requirements
All the Washed samples are kept in oven for drying at 100–110 °C temperature for 24 hours duration. The ratio used for preparing mortar consists 1 part by weight of cement and 2.25 parts by weight of dry aggregate. For three prisms of dimensions (25×25 ×285 mm), the amount of cement and dry aggregate required is 440g and 990 g. For each aggregate source, three prisms were moulded. The W/C ratio used for mortar preparation was 0.47. Mortar ratio of 1: 2.25 is used for aggregates whose relative density is above or equal to 2.45. Aggregates which have relative density (OD) < 2.45, the aggregate ratio is determined as follows: Aggregates ratio = 2.25 x (Relative density of aggregates to be tested) / 2.6 Table-4: Amount of material for three mortar prism Cement Type
Aggregate Source
Cement, gm
Aggregate, gm
Water, ml
W/C ratio
OPC
A
440 gm
990 gm
206 ml
0.47
OPC
B
440 gm
990 gm
206 ml
0.47
Fig.-1: Mortar Bar prisms casting Digital dial guage having the scale interval of 0.001 mm is used to measure the linear expansion of specimen. The dial gauge was fixed with in the frame. Specimen is held between frame and indicator axles into the gauge studs present at the ends of the specimen. For performing the test, three prisms were moulded for each aggregate source. After moulding and hardening of prisms, they are immersed into water in air tight container at 80C for 24 hours as shown in (Figure 2). The specimens are removed from water and distance between the ends of the gauge studs is taken with the help of length comparator. This reading is recorded as zero reading (L0).This zero reading is regarded as reference reading for further comparison of specimen expansion. After that the mortar specimens are placed in sodium hydroxide solution of 1M molarity in air tight micro-wave containers (Figure 3). These Containers are placed into climatic chamber (Figure 4) where 80C temperature is maintained. After placing specimens into 1 M sodium hydroxide solution at 80 C, the specimen dimensions (Ln) are recorded at least three times in 14 days period (5).
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Fig.-2: Mortar bars placed in water
Fig.-3: Length comprator
Fig.-4: Climatic chambers The linear expansion of each specimen is obtained as follows Expansion, % = 100 x (Ln − L0) / l Where: Lo - Zero reading i.e. reading of prisms before placing it into sodium hydroxide solution Ln – Reading at each interval after placing it into sodium Hydroxide solution, where n represents the interval l - Distance between the ends of the gauge studs, measured to the nearest of 0.1 mm (5).
IV.
TEST RESULTS AND ANALYSIS
The test ASR of crushed gravel source A and B, with OPC cements after 14 days gave the results which are presented in Figure 5 and Figure 6.
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A Aggregate source 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 A aggregate Fig.-5: Source A crushed gravel Expansion graph B aggregate source 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0
E X P A N S I O N
1 2 3 4 5 6 7 8 9 101112131415 DAYS
B aggregate source Fig.-6: Source B crushed gravel Expansion graph C0MPARISON 0.1
E X P A N S I O N
0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0 0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15
DAYS
A Aggregate source Fig.-7: Comparison of Source A and B crushed gravel Expansion graph The expansion of crushed gravel source A after 14 days was found to 0.0261%. However the expansion of crushed gravel source B after 14 days was found 0.0420%. Both the crushed gravel sources have expansion below the limit of ASTM C 1260 i.e. 0.2%. www.irjmets.com
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e-ISSN: 2582-5208 International Research Journal of Modernization in Engineering Technology and Science Volume:03/Issue:02/February-2021
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V.
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CONCLUSIONS
Expansion of both A and B crushed gravel sources placed in sodium hydroxide solution of 1M molarity at 80C temperature after 14 testing days didn’t exceeded the linear expansion limit 0.2 % according to ASTM C-1260 method. Hence, we can say that both crushed gravel aggregate A and B are not reactive and are indicative of innocuous behavior. Also the linear expansion was below from 0.1%, so there was no need to increase the testing time beyond 14 days. Hence As per ASTM C 1260 research methodology both A and B crushed gravel sources with OPC cement are safe for ASR.
VI.
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