AN EVALUATION ON TS-10465 AND TS EN 12504/1 FOR THE DETERMINATION OF COMPRESSIVE STRENGTH OF HARDENED CONCRETE

İmalatı tamamlanmış betonarme yapılara ait yapı elemanlarının basınç dayanımlarının tayin edilmesi için, tahribatlı bir deney yöntemi olan karot numunesi alınması ve tahribatsız bir deney yöntemi olan yüzey sertliği metodu, yaygın olarak ayrı ayrı veya birlikte kullanılmaktadır. Ülkemizde, sertleşmiş betondan karot alınması ve test edilmesi ile ilgili temel hususlar, TS 10465 ve TS EN 12504/1 standartları ile belirlenmiştir. Halen yürürlükte olan bu standartlarda belirtilen numune alma yöntemi ve hesap esasları ile ilgili önemli tereddütler mevcuttur. Bu çalışmada, ilgili standartlar irdelenerek, bu standardın eksiklikleri ve çelişkileri ortaya konulmuş ve çözüm önerileri sunulmaya çalışılmıştır. Yapı stoğunun çoğunu betonarme yapıların oluşturduğu ve mevcut yapıların yapısal dayanımları ile ilgili ciddi şüphelerin var olduğu ülkemizde, bu standartça önerilen yöntemler ile yapılan analizler çok büyük önem taşımaktadır. Dolayısıyla bu standart ile ilgili oluşan tereddütlerin ortadan kaldırılması, bu konu ile ilgili çalışan mühendislerimizin daha doğru değerlendirme yapabilmesini sağlayacaktır. In order to determine the compressive strength in structures components of finished reinforced concrete systems, the destructive method of obtaining core samples and the non-destructive method of surface hardness method are widely used separately or together. In Turkey, basic principles about obtaining samples in hardened concrete in structures and the tests applied are based on TS 10465 and TS EN 12504-1 standards. However, there seems to be serious conflicts in these standards about the method for obtaining samples and their calculation principles. In this study, considering these standards, existing drawbacks and uncertainties were emphasized and related solution proposals were presented. Accounting the percentage of reinforced concrete structures in our country, these standards become more crucial; thus, it is essential to remove these serious doubts about considered strength analyzing methods for helping our engineers to evaluate in a better way

ABRASION RESISTANCE ESTIMATION OF HIGH STRENGTH CONCRETE

This study gives the results of a laboratory investigation undertaken to determine the relationship between mechanical properties (compressive and flexural strengths) and abrasion resistance of 65-85 MPa high strength concretes incorporating silica fume, fly ash and silica fume-fly ash mixtures as supplementary cementing materials. A series of six different concrete mixtures including a control high strength concrete mixture (C1), and five high strength concrete mixtures (C2, C3, C4, C5, C6) incorporating supplementary cementing materials, were manufactured. The compressive strength, flexural strength, and abrasion resistance were determined for each mixture at 28-days. Mathematical expressions were suggested to estimate the abrasion resistance of concrete regarding their compressive strength and flexural strength

THE EFFECT OF AGGREGATE MAXIMUM SIZE ON IMPACT RESISTANCE OF FIBER REINFORCED CONCRETE

In this study, the effect of maximum size of aggregate on impact resistance of fiber reinforced concrete were investigated. Using crushed limestone aggregate with 10, 15, 20 and 25 mm of maximum size, 8 different normal-steel fiber reinforced concretes were produced. Water/cement ratio and cement dosage of concrete mixtures are 0.5 and 400 kg/m3, respectively. Hooked-end bundled steel fibers with l/d ratio of 65 and 1.0% fiber volume were used in fiber concretes. After 28 days standard curing, compressive strength, split tensile strength and ultrasonic pulse velocity tests were performed on 150/150/150 mm cube specimens. Additionally, impact resistances of concrete specimens were determined using impact test apparatus described in ACI 544.3R-93. 150x300 mm cylinders were prepared for impact resistance tests. After 28 days curing, these specimens were cut and 150x64 mm special discs were prepared. Impact resistance test were performed on these special discs. Experimental results were evaluated corresponding to presence of steel fiber and aggregate maximum size

YÜKSEK DAYANIMLI BETONDA AŞINMA DİRENCİNİN TAHMİNİ

Bu çalışmada, silis dumanı ve/veya uçucu kül içeren basınç dayanımı 65-85 MPa olan yüksek dayanımlı betonların, aşınma direnci ile mekanik özelikleri (basınç ve eğilme dayanımı) arasındaki ilişkiyi belirleyebilmek amacıyla yapılan deneysel çalışma sonuçları sunulmuştur. Bir adet yüksek dayanımlı beton kontrol karışımı (C1) ve beş adet katkı içeren yüksek dayanımlı beton karışımı olmak üzere (C2, C3, C4, C5, C6), toplam altı adet beton karışımı hazırlanmıştır. Tüm karışımların 28 günlük basınç dayanımları, eğilme dayanımları ve aşınma dirençleri belirlenmiştir. Betonların basınç ve eğilme dayanımına bağlı olarak aşınma direncini tahmin eden matematiksel eşitlik önerilmiştir

Effect of different parameters on concrete-Bar bond under high temperature

© 2014, American Concrete Institute.Exposed temperature level is one of the important parameters for concrete-bar bond in reinforced concrete. Subjecting reinforced concrete to high temperature, as in fire, leads to loss in concrete-bar bond. Environmental factors also can be stated as temperature level, heating rate, and heating time. In this study, the effects of temperature level, concrete cover, and mechanical properties of concrete on concrete-bar bond have been investigated in different concrete classes. Concrete strength, concrete cover, and temperature level were chosen as parameters. Pullout and mechanical tests were conducted on the specimens exposed to 20, 300, and 500°C (68, 572, and 932°F). As a result, it was seen that as concrete cover increases, concrete-bar bonds were less affected by high temperature. Furthermore, the empirical relationship between the experimental pullout loads and parameters has been defined

Use of recycled mortar as fine aggregates in pavement concrete applications

The use of recycled aggregates derived from construction and demolition wastes increased in the concrete construction industry. While the coarse fraction (i.e., from 5 to 20 mm) was successfully recycled, the fine fraction (i.e., from 0 to 5 mm) is hardly recyclable given its heterogenous nature and poor physical properties. This paper assesses the feasibility of recycled mortar aggregate (RMA) in pavement concrete applications requiring superior resistance to weathering and wearing effects. Three concrete strength grade categories prepared with different water-to-binder ratios (w/b) of 0.4, 0.5, and 0.6 are investigated; the natural sand replacement levels by RMA varied from 0 % to 60 % by volume, at 20 % increment rates. Test results showed that the detrimental RMA effect on durability depends on the concrete strength category, requiring proper adjustment of the maximum replacement rate to maintain acceptable losses in performance. Hence, the higher strength grade mixtures prepared with 0.4 w/b were found to yield significant drops in durability reaching 25 % in water sorptivity, 18 % in abrasion, and 22 % due to freeze/thaw (F/T) cycles. In contrast, the lower strength grade concrete made with 0.6 w/b exhibited marginal degradation in strength and durability, despite the incorporation of 60 % RMA. The resulting losses in sorptivity, abrasion, and F/T cycles were limited to 13 %, 8 %, and 12 %, respectively