Service life of concrete structures

Concrete is a porous material. The size and distribution of pores in concrete varies, depending upon the quality of compaction, the materials, the water-to-cement ratio and the degree of hydration. Many of these pores are inter-connected creating larger and more complex pore systems. Water can penetrate this network and cause deterioration of the concrete structure. Silanes have been generally used in the past to help protect reinforced concrete exposed to an aggressive environment. The treatment works as a pore liner, thus ...

The need for alternative cementing materials to ordinary Portland cement (OPC) has promoted characterization research on pozzolana as an important ingredient in cement production. In Uganda, natural pozzolana application in cement production is done by only two producers of Portland cement and at a small scale due to capacity constraints. The capacity constraints, together with other technological issues, continue to hinder realization of the cost reduction and improved quality benefits attributed to the use of pozzolana as a mineral admixture in Portland cement concrete. There is high abundance of natural pozzolana in Uganda in the form of volcanic ash/tuffs which, if adequately characterized, can facilitate production of different cementing materials and increased output from the various players in the cement production industry in Uganda. This paper reviews methods of pozzolana characterisation and presents preliminary research findings on application of natural pozzolana sourced from Uganda in development of Portland cement concrete. Samples collected from two different deposits in the western region of Uganda were prepared and subjected to chemical analysis and tests on compressive strength, flexural strength and flow-ability. The preliminary findings are indicative of good quality pozzolanic materials that can be applied in production of Portland pozzolana cement materials.

Key words: Characterization, Portland pozzolana cement, volcanic ash, natural pozzolana, Uganda

Comprehensive study was made of compressive and flexural strengths by different
types of portland cement used in concretes mixed, placed, and cured at various
temperatures, and includes tests indicate that there is a temperature during the early
life of concrete which is considered optimum with regard to strength at later ages.
This objective provides an overview of the effects of temperature on the behavior of
concrete materials and structures. In meeting this objective the effects of temperatures
as it elevates and depresses from ambient temperature, are worked out.
This paper also deals with the procedure and precautions to be observed while
concreting in extreme weather conditions- hot and cold weather so as to minimize the
detrimental effects of weather on concreting in general types of construction, such as
buildings, bridges, highways, pavements and other similar structures.

High Performance Concrete (HPC) is now a days used widely in the construction industry worldwide. To produce HPC with normal ingredients one use mineral admixtures like silica fume, fly ash and metakoline. In addition admixtures including Superplasticisers are also used. This paper investigates the effect of silica fume (SF), added in varying percentages (0, 3, 5, 7.5, 10, 12.5%), on concrete strength. Superplasticiser-(Viscocrete Tempo 12)-was added to the concrete mixtures as well. Compressive strength, shear strength and tensile strength tests were conducted, and the results were discussed. Results showed that the compressive strength changes with the varying percentage addition of silica fume. The highest compressive strength (88 MPa) was obtained when the percentage of silica fume was 7.5 % of the cement weight. Beyond 7.5 % silica fume, the compressive strength started descending. Tensile and shear strength were found to vary in an inverse relationship with the increasing percentage of silica fume. A significant reduction in tensile strength and shear strength were recorded when the silica fume percentage is increased. However, the 10% ratio between tensile and compressive strength for normal concrete, was not found to be, relevant for HPC with SF.

The matrix mixture of concrete can be made to have high compressive strength. In the present paper, statistical model was built-up to predict the compressive strength of concrete containing different matrix mixtures at fixed age or at different age of 1, 3, 7, 28, 56, 90 and 180 days. The model examines eight different parameters for the matrix mixture that includes: time, water, cement, metakaolin (MK), silica fume (SF), sand (S), aggregate (A)
and superplasticizer (SP). This research addresses the effect of the matrix mixture of concrete on the compressive strength, where this information will help the cement industry in producing the required concrete strength. The results from the predicted model have high correlation to the experimental results for the concrete compressive strength.

Bu kitabın amacı; İstanbul ve çevresi taş-doğal agrega ocaklarını böyle bir kitapcıkta toplamak ve genelde sağlam, dayanıklı ve ekonomik yapıların inşaasında kullanılması zorunluluğu olan bu taş ve kum ocaklarının özelliklerini göz önüne kayarak, inşaaat sahibine, kullanıcıya, yapımcıya ve kontrol edenlere bir ışık tutmaktır. Kullanım alanlarının çok geniş olması ayrı özenle seçilmelerini gerektirmektedir.
Kitapta taş ve kum hakkında genel bilgiler verilmiştir. Ayrıca İstanbul civarı taşocakları Anadolu ve Rumeli taşocakları olarak iki ayrı grupta ele alınmıştır. Bu ocaklardan elde edilecek agregaların fiziki, mekanik ve petrografik özellikleri verilmiştir.
Günümüz yasaları göz önünde bulundurularak yeni bir taş ocağı açılımı sırasında takip edilecek yolun seçimi ve işletilmesinde lüzümlu tavsiyeler de bu kitapta verilmiştir. Necat CİLASON 1989.

Ülkemiz genelde özellikle kıyı kesiminde Akdeniz iklimi yaşamaktadır; deniz tuzluluğu % 2.5-3.5 arasındadır.

Körfez olan yani suyun durgun olduğu kesimlerde bu oran daha da yükselmektedir. 1973 yılından itibaren önce İran körfezi, Kızıldeniz ve sonra Akdeniz kıyılarında yeni inşa edilen betonarme yapılarda 3-8 yıl gibi çok kısa bir sürede önce çatlama ve sonra betonun donatıdan ayrılarak kopması gibi korkunç bir durum gözlenmiştir. Yapılan geniş çaplı araştırmalar bu hastalığın nedeninin deniz suyundaki tuz (sodyum klorür) dan olduğunu meydana çıkarmıştır. Uluslararası çalışmalar, önce yıllardır deniz suyuna karşı betonu dirençli kılacak diye düşünülen ama bunun tam aksi donatı korozyonuna yol açan, sülfatlı sulara dayanıklı ve içindeki C3A (Trikalsiyum aluminat) miktarı % 5 ten az olan çimentonun deniz kıyısı yapılarda kullanılmaması neticesine varmıştır. Bu tür korozyon ile ABD de hasar yıllardır bilinmekte idi. Orada, kış aylarında yol, otoyol köprüleri üzerindeki buzlanmayı önlemek için kullanılan klorür esaslı tuzlar, betonun içine girerek donatıyı koruyacak olan pas payındaki betonun pH ını düşürerek alkalinitesini azaltıp donatıya vararak paslanmaya (korozyona) sebebiyet verimiştir.

Yıllar ve araştırmalar ilerledikce bilhassa sıcak iklim bölgelerinde korozyona uğramış yapıların onarım ve rehabilitasyonunda önce bir inceleme yöntemi ile korozyon bölgesinin derinliklerinde şiddetin tespiti ve bundan sonra bu aşamada yeterli olan metod ve malzemelerin kullanılması tekniği geliştirilmiştir. Ayrıca yeni yapılarda korozyonu önlemek amacıyla beton katkıları ve donatı koruyucuları bulunmuş ve 1996 yılından itibaren sıcak iklimli bölgelerde kullanımı başlamıştır.

Uluslararası Yapı Malzeme Deneme Araştırma Laboratuvarları Birliği (RILEM), Kanada ve Amerika Beton Enstitüsü, Almanya, Danimarka ve İskandinav ülkeleri Üniversite ve birlikleri bu konudaki otoriteleri ile yoğun çalışmalarını sürdürmektedir. Lakin henüz korozyona karşı kullanılması uygun çimento tipi, agrega ve katkı malzemeleri için bir teknik şartname veya standard üretilmemiştir. Herşey tavsiye ve öneri niteliğindedir.
Yurdumuzu mateme boğan 17 Ağustos 1999 depremi sonrası yapılan gözlemler, kıyı şeridindeki Gölcük, Yalova ve İzmit yerleşimindeki yapılarda depremden önce korozyon nedeniyle büyük çapta hasarların mevcudiyetini ortaya çıkarmıştır.

I. kısım STFA Kalite Ekspertiz ve Gözetim Ltd. Şirketinin 1985 yılından itibaren gerek şantiyelerde gerekse merkez laboratuvarda yaptığı çalışmalar, hazırladığı raporlar ve konferans bildirileri ışığında hazırlanmıştır.

Kitabın II. kısmı RILEM CHC–94 – Sıcak İklimlerde Beton Komitesinin 6 yıllık çalışmalarını kapsamaktadır. Yazarlardan Necat CİLASON bu komitenin sürekli çalışan 9 üyesinden biri olmuştur.

Kıymetli vaktini bizden esirgememiş, (tatil yaptığı zamanda) kitabi satır satır okumuş ve yılların birikimi, bilgi, görüş ve tavsiyelerini belirtmekle çok kıymetli katkıda bulunan sayın hocamız Prof.Dr. Süheyl AKMAN’a minnet ve şükran borcumuz çok büyüktür. Sağ olsun, var olsun.

Editör incelemesinden sonra kitabın yeniden yazılımında dikkat ve sabır ile katkıda bulunmuş olan İnş.Y.Müh. O.Belgan ONAT’a da teşekkür ediyoruz.

Kitabın, Ülkemizde, yapı malzemeleri, beton, çimento , kum+çakıl ve katkı ve kür malzemeleri ile uğraşanlara, üniversitelerimizdeki öğrencilere, araştırma kuruluşlarına ve Türk Standartlar Enstitüsünün bu konudaki çalışanlarına faydalı olmasını dileriz. Eylül 2000.

Corrosion of the steel reinforcement in concrete requires manual and costly repair procedures to prevent premature failure of constructions. Although preventive measures during the construction phase are often implemented, such as application of a several cm-thick concrete cover layer, early corrosion may still occur. The primary reason for premature corrosion is crack formation in the concrete cover. Larger cracks as well as a network of finer cracks allow water, oxygen, chloride, and other aggressive corroding substances to penetrate the concrete matrix to reach the reinforcement. The objective of the paper described in this proposal is the development and application of a bio-chemical agent which, when incorporated in the concrete matrix, autonomously and actively prevents premature reinforcement corrosion in a twofold mode. The bio-chemical agent, consisting of a mixture of bacteria and calcium lactate, produces when activated by ingress water calcium carbonate-based minerals by metabolic conversion of calcium lactate. The produced bio-minerals block and seal cracks resulting in a delay of further ingress of water as well as to a decrease of inward diffusion rate of chloride and oxygen. Moreover, as the metabolically active bacteria consume oxygen, the agent acts as an oxygen diffusion barrier protecting the embedded passivity steel reinforcement against corrosion. In this way the reinforcement will be protected for substantially increased periods, even after breakdown of the passivity layer, as a lack of oxygen prevents further corrosion. Incorporation of the agent in concrete will be relatively cheap as well as easy when the agent is immobilized in porous light-weight aggregates prior to addition to the concrete mixture. It is expected that the application of the proposed sustainable bio-chemical healing agent will result in substantially decreased maintenance and repair costs of steel-reinforced concrete structures.

In this study, constitutive relationships are developed/or normal-strength concrete (NSC) and high-strength concrete (HSC) subjected to fire to provide efficient modeling and specify the fire-performance criteria for concrete structures exposed to fire. They are developed for unconfined NSC and HSC specimens that include compressive and tensile strengths, compressive elastic modulus, and compressive and tensile stress-strain relationships at elevated temperatures. The proposed relationships at elevated temperatures are compared with the experimental results and previous existing relationships revealing several advantages and disadvantages of present stress-strain relationships. These results are used to establish more accurate and general compressive and tensile stress-strain relationships. Further experimental results for tension and the other main parameters at elevated temperatures are needed to establish well-founded models and improve the proposed constitutive relationships, wh...

Formation of cracks can be often visible in concrete structures. Although small cracks hardly affect structural properties of a construction, but they increase permeability, which in itself reduces structural stability and threatens structural durability, especially in humid environments.The risk of cracks in concrete structures based in humid environment, such as concrete dams and spillways, is much higher. Concrete repair is a complex process that differs greatly from the recently applied technologies in concrete structures construction. In concrete repair, new materials should be combinedwith old materials in such a way that a suitable combination is obtained able to maintain structures durability over the time against the environmental factors. There are different methods of concrete cracks repair. In the present article we will review several methods for treating concrete cracks.

Mining and quarrying activities in Europe generate approximately 55% of total industrial wastes, according to a recent Eurostat report. Most of these wastes are directly dumped on land or deposited in landfill sites. The first solution may lead to negative environmental impacts on land (removal of vegetation, deforestation, land slope changes and increased risk of erosion), water (pollutant transport through surface runoff, soil infiltration and contamination of water resources), may lead to the contamination of agricultural goods and may impose risks on human health. In Portugal, about 20% of industrial waste produced originates from mines and quarries, particularly from Panasqueira mining, one of the largest tungsten mines in the world. Currently, Panasqueira mining generates almost 100 tonnes of waste-rock, per day. Such waste-rock have accumulated over a number of years into very large heaps and it is desirable to seek new economic solutions that can contribute towards their reuse. In this context, this work discusses the potential for reuse of waste-rock piles of Panasqueira tungsten mine, which may be a case statement to be followed. The proposed solution described in this paper consists in developing innovative polymer-based composite materials, obtained from non-contaminated waste-rock tailings. Such materials must have suitable properties for technical-artistic value added applications, such as conservation, restoration and/or rehabilitation of historic monuments, sculptures, decorative and architectural intervention, or simply as materials for building revetments.

In the current study it is investigated the possibility of use of wolframite and stibnite ore from Lachanas area, Northern Greece, as flux agent in the production of cement. The stibnite and wolframite deposits of that area are typical of the Sb-W type of mineralization. The Sb ore occurs more massive and volumetrically more extended than W ore.  The ore bodies have been partially altered to secondary minerals of oxidation zone. The neoformed minerals have affected the original Sb and W content of the ore. However the oxidation of the deposit does not affect its use as flux agent in cement industry. It is well known that the most energy demanding stage in the cement industry is the sintering process. It has been found that certain additives may accelerate the sintering reactions and improve the reactivity of the cement raw mix. The minerals, iron rich wolframite, stibnite and a wolframite-stibnite assemblage were selected in order to introduce W, Sb and S in the cement raw mix. One reference sample and 12 test samples prepared by mixing the reference sample with the above minerals in 0.5, 1.0, 1.5 and 2.0% w/w were studied. The effect on the reactivity of the raw mix is evaluated on the basis of the un-reacted lime content in samples sintered at 1000, 1100, 1200, 1300, 1350, 1400 and 1450oC. It is concluded that minerals containing Sb promote the consumption of the free lime, in the most effective way. The XRD studies, performed in samples that were burned at 1450oC, showed that the diffraction patterns correspond to a structure of a typical clinker, obtained at the above temperatures.

- Greek Abstract
ΠΕΡΙΛΗΨΗ
Στην παρούσα εργασία μελετάται η δυνατότητα χρήσης βολφραμίτη και αντιμονίτη από την περιοχή του Λαχανά στο μίγμα παραγωγής κλίνκερ με στόχο τη μείωση της ενεργειακής απαίτησης κατά την έψηση. Το παραπάνω μετάλλευμα αντιπροσωπεύει ένα από τους χαρακτηριστικούς τύπους μικτών κοιτασμάτων Sb-W. Το μετάλλευμα του Sb γενικά εμφανίζεται πιο συμπαγές και σε σημαντικότερα μεγαλύτερα ποσά σε σχέση με το μετάλλευμα W. Τόσο ο αντιμονίτης, αλλά κυρίως ο βολφραμίτης έχουν οξειδωθεί μερικώς, με αποτέλεσμα την μετακίνηση στοιχείων και τον σχηματισμό οξειδίων και άλλων δευτερογενών ορυκτών, που επηρεάζουν την ποιότητα των υλικών ως προς την τελική τους περιεκτικότητα σε W και Sb. Εν τούτοις η οξείδωση των μεταλλευμάτων δεν οδηγεί κατ’ ανάγκην σε ακαταλληλότητα χρήση τους ως ευτηκτικό υλικό για την παρασκευή κλίνκερ. Προέκυψε ότι Το φυσικό μίγμα βολφραμίτη-αντιμονίτη και ο αντιμονίτης ευνοούν την έψηση του μίγματος των πρώτων υλών και η θετική αυτή επίδραση αυξάνεται με την αύξηση έως και 2% του ποσοστού συμμετοχής τους. Το μίγμα βολφραμίτη-αντιμονίτη είναι αυτό που παρουσιάζει τη βέλτιστη συμπεριφορά.

It is suitable to use precast steel-concrete composite beams to quickly assemble a bridge or a building, particularly in isolated regions where cast-in-situ concrete is not a practical option. If steel-concrete composite beams are designed to allow demountability, they can also be extremely useful in the aftermath of natural disasters, such as earthquakes or flooding, to replace damaged infrastructure. Furthermore, rapid replacement of slabs is extremely beneficial in case of severe deterioration due to long-term stressors such as fatigue or corrosion. The only way to rapidly assemble and disassemble a steel-concrete composite structure is to use demountable shear connectors to connect/disconnect the steel beams to/from the concrete slab. In an attempt to respond to this demand, recent research developed a removable Friction-Based Shear Connector (FBSC), which eliminates slippage in the steel-concrete interface at SLS (i.e. it offers full-interaction). This paper describes the experimental program that assessed the flexural behaviour of a 9.0 m precast steel-concrete composite beam equipped with FBSCs. The design of the composite beam was based on a 32% degree of partial shear connection, i.e. considerably below the minimum degree specified in Eurocode 4. The paper gives a detailed account of the test results that clearly show that the composite beam with the FBSCs is effective and has properties that match design needs for both SLS and ULS verifications.

Formation of cracks can be often visible in concrete structures. Although small cracks hardly affect structural properties of a construction, but they increase permeability, which in itself reduces structural stability and threatens structural durability, especially in humid environments.The risk of cracks in concrete structures based in humid environment, such as concrete dams and spillways, is much higher. Concrete repair is a complex process that differs greatly from the recently applied technologies in concrete structures construction. In concrete repair, new materials should be combinedwith old materials in such a way that a suitable combination is obtained able to maintain structures durability over the time against the environmental factors. There are different methods of concrete cracks repair. In the present article we will review several methods for treating concrete cracks.

The decision to perform an extraordinary maintenance or a seismic retrofit of existing RC buildings should be based on rational criteria, which lead into account a number of factors that are able to define the cost-effectiveness of the investment. Among them the age of the concrete structure and its normal depreciation are key. The paper proposes value-time functions for the two main depreciation factors: age, and income decay. Empirical formulas have been developed to estimate the economic life of concrete structure on the basis of analysis of these depreciation functions.

This study is included the initial findings of comprehensive research project on mechanical properties of mortar with
boron modified active belite cement (BAB) and resistance effectivity against corrosion of steel reinforcing bar
embedded BAB cement mortar. The compressive and flexural strength tests conducted to determine the mechanical
properties of mortar specimens having dimension of 40x40x160 mm in the investigation. Besides, the electrochemical
tests applied on the cylindrical specimens having dimension of φ50x100 mm at the ending of exposed to 5% NaCl
solution for 60 days. Five specimens were produced for every test on two trial groups.

Concrete resistivity is directly related to relative humidity (RH) and is also affected by temperature. In this paper, a theoretical discussion about how these two factors affect resistivities of concrete and mortar is provided. Moreover, experimental results on sensorized mortar probes are presented and correlated to analytical models of temperature and humidity influences. All measurements were performed under controlled conditions. Temperature, RH, and resistivity were measured simultaneously in a particular zone of the probes. Temperature scanning was performed over short periods of time (approximately 1 h) and the probes were covered with waterproof paraffin each time for constant humidity content. This was feasible as all sensors were embedded. Water contents were ensured during the experiment by weighting the probes. Conclusions on the applicability of these techniques, their advantages, and limitations, and correlation to Archie and Arrhenius laws of the results are made.