Ενανθράκωση με διάβρωση

[agior]

νιώθω απλά μαλ@κ@ς... Ισως η δικαιολογία μας να είναι η τότε περιορισμένη πρόσβαση στην πληροφορία.

[Ροδοπουλος]

Πες μας γιατί?

Για κατσε πιστευεις οτι ο κόσμος στα πανεπιστήμια δεν τα ηξερε? Πιστεύεις οτι εργαστηρια σκυροδεματος δεν το έχουν ή ειχαν? Πιστευεις οτι κανενα εργαστήριο μαθηματος δεν θα επρεπε να τα δείξει στον φοιτητη? Μηπως στο εξωτερικό ειναι καλυτεροι? Δεν ξερω ρε παιδια.

 

διαχυση χλωριόντων

συγκεντρωση χλωριόντων σε σχεση με την αποσταση απο την θαλασσα. Για να εχετε μια εικόνα.

 

διαβασμα

 

Construction materials: their nature and behaviour

 

Μαθημα

Λοιπον εφτιαξα καφε και πισω στο μαθημα.

 

Οπως καταλαβαινεται ειμαι λιγο ανορθοδοξος. Πρωτα σας λεω τι θα παθαινει το ΩΣ και μετα σας παω πισω στην θεωρια. και ξανα στην παθογενεια. Για 16 χρόνια δουλευει ή πιστευω οτι δουλευει.

 

Παμε παλι.

 

Σας εχω παρει τα αυτια για τους πόρους, σανιδια, permeability, porosity, αποστατες, W/C και Χασαν κλπ.

 

ΓΙΑΤΙ ?

Φωτο

 

carbonation2

 

 

Εδω βλεπουμε την ρυγματωση σε σχεση με την ενανθρακωση. Προσοχη η κλιμακα ειναι 30 και οχι 50 χιλιοστα. Τωρα η ιστορια

 

Το σχημα που βλεπετε ειναι τυπικό ενανθρακωσης. Ποτε δεν ειναι ομοιόμορφη διοτι οι δρομοι διαχυσης δεν ειναι ομοιόμορφοι. Τωρα κοιταξτε και δειτε την εικόνα

 

presentation 1

 

τωρα το άλας ανθρακικού ασβεστίου επανακρυσταλλώνει και αποροφά επιπλεον υγρασία. Οι κρυσταλλοι εχουν σχεδόν διπλασια ογκο σε σχεση με το ογκο του τσιμεντοπολτου που κατεβαλαν. Εαν ομως η θερμοκρασια ειναι > 32 βαθμοι τοτε ο ογκός ειναι τριπλασιος. Οι κρυσταλοι μπορεί να ειναι τοσο μεγαλοι οσο και το χαλικι. presentation 2

 

Τωρα εαν εχουμε κα πόρους οι οποίοι συσσωρευουν υγρασια τοτε αυτοί γεμίζουν με κρυσταλους.

 

presentation 3

 

Τωρα εαβ οι ποροι που συνηθως ειναι περιμετρικα στα χαλικια γινουν κρυσταλοι και αυξησουν τον ογκο τους τοτε εχουμε περιμετρική αποκολυση presentation 5.

 

Τωρα εαν εχουμε ολα αυτα ο συντελεστης θερμικης διαστολης του σκυροδετος αλλάζει (αυξανει τοπικά) με αποτέλεσμα περαιτέρω ρυγματωση. Περαιτέρω ρυγματωση ευκολοτερη διαχυση, κλπ. Καταλαβαινεται οτι προκειται για αλυσιδωτη αντιδραση και ενας καρκίνος.

 

Ελεγχος ενανθρακωσης

Μια τεχνική που χρησιμοποιούν πολλοί μηχανικοί ειναι ο ψεκασμός με δεικτη ενανθρακωσης. Κατα βάση ο αριθμός τω μετρησεων που θα πρεπει να γινει ανα στοιχείο ειναι μεγάλος με αποτελεσμα ενας ψεκασμος να μην μας δωσει απαραιτητα το προβλημα (τυχαιο γεγονός). Θα πρεπει να κανουμε μετρήσεις Πεχα ή ενδοσκοπική μέτρηση πεχα οπως εχω πει προηγουμένος.

 

Κρουσιμετρο και υπέρηχος

 

Ενα απο τα προβλημα που θα αντιμετωπίσουμε με τον ΚΑΝΕΠΕ ειναι η τριλογία

 

κρουσίμετρο, υπερηχος και θλιψη πυρήνα.

 

Στην εικόνα βαζε αποτελέσματα κρουσιμέτρησης και υπερήχου.

 

Απο το στοιχείο πηραμε εναν μονο πυρήνα Φ100 με μήκος 100 χιλ. Η αντοχή του ηταν 24. Ποιος έχει δίκιο?

 

Λοιπόν να ξεκαθαρίσουμε καποια πραγματα.

 

1. Η κρουσιμέτρηση γινεται πάντα μπροστά απο οπλισμό. Αρα θα πρέπει να εχουμε πρωτα μαγνητογραφία.

 

2. Η κρουσιμέτρηση ειναι ευαισθητη στην επιφανεια. Πρωτα καθαρισμός με τροχό.

 

3. Η κρουσιμέτρηση παντα στις 90 μοιρες. Προσοχη ενα καλό κρουσίμετρο εχει offest γωνίας.

 

4. Ο υπέρηχος ειναι ευαισθητος στο ογκο που σκανάρει. Επίσης χρειάζεται καλιμπραρισμα. Ενας καλός εχει βαση δεδομένων.

 

5. Ενας καλός υπέρηχος εμφανίζει πυκνότητα σηματος. Απο την κυματομορφή παιρνουμε την ακρίβεια. Εαν εχουμε διακοπή ή διακοπές σηματος τοτε α) εχουμε ρυγματωση β) εχουμε αλλα πραγματα (τουβλο, ξυλο, αφρολεξ, κλπ.) Σιγουρα επιλέγουμε περιοχές με μικρή διακοπή.

 

6. Η θλιψη εχει τα δικά της προβληματα. Ξεκιναμε απο την προετοιμασία του δοκιμίου, της βασης δοκιμίου. Θα πρεπει να δουμε να τηρειται το ASTM C39 and C617.

 

7. Η θλίψη εχει το προβλημα της δειγματοληψίας. ποσα ? και απο πού?

 

8. Δεν θα μπορούσα να παρω πυρήνα απο το σημειο 9 της εικόνας με την μικροτερη αντοχή.

 

9. Τωρα εαν το σκυροδεμα ειναι ενανθρακωμένο σε βάθος 30 χιλιοστών τότε η θλίψη δεν θα το δεί. Το βλεπει ομως ο υπέρηχος και η κρουσιμέτρηση. Δηλαδή η θλιψη δεν ειναι ευαισθητη στην ενανθρακωση.

 

10. Τι κάνουμε. Εγω χρησιμοποιω κατι απλο. Λεω θελω την μινιμουν τιμή απο κρουσιμέτρηση 21, την μινιμουν απο υπερηχο 23 και την θλιψη 24. Εαν εχουμε διαφορά μεγαλυτερη απο το συν πλην 15% της τιμής του υπερήχου και των κρουσιμετρησεων και θλιψης τοτε δινω ευρος αντοχής το μικρότερο. Εαν εχουμε μικτοτερο τοτε δινω την τιμη του υπερηχου. Στα Ελληνικά προτυπα μιλανε για στατιστική αναλυση. ο προβλημα που εχω ειναι οτι ο αριθμός δειγματος κρουσιμέτρησης και υπερηχου ειναι πολύ μεγαλυτερος απο αυτων των θλιψεων. Αρα στατιστικά δουλευω με ισχυρα διαφορετικό δειγμα.

 

Control of Cracking in Concrete Structures

 

βαζω ενα λινκ για διαβασμα

 

http://www.concrete.org/General/f224R%2801%29Chap3.pdf

 

διαβασμα

repair of concrete structures to EN 1504: a guide for renovation of concrete

 

Ενα φοβερο μαθημα

 

ρωτησα τον φιλο μου Edward να τα βάλει σε λινκ για σας

 

http://www.hkis.org.hk/hkis/html/upload/CPDLink/2007034.pdf

 

καταβαστε το και διαβάστε το.

 

Το μανουαλ

http://www.ietcc.csic.es/fileadmin/Ficheros_IETcc/Web/EventosPublicaciones/PublicacionesElectronicas/manual_ingles.pdf

 

Πειτε μου εαν σας ενδιαφερει να συνεχισω

 

Παιδια αισίος ειμαστε στα 340 μηνυματα. θελετε να παμε πιο βαθειά ή μαθατε αρκετα?

[Αλέξανδρος]

Δώσε μπάρμπα!!!!!!!!!!:D:D

[Ροδοπουλος]

ASR

 

paste it on your browser

 

ocw.kfupm.edu.sa/user/CE30301/Lectures%20No9-10-webCT.ppt

 

Shrinkage in concrete

 

Concrete is subjected to changes in volume either autogenous or induced. Volume change is one of the most detrimental properties of concrete, which affects the long-term strength and durability. To the practical engineer, the aspect of volume change in concrete is important from the point of view that it causes unsightly cracks in concrete. We have discussed elsewhere the effect of volume change due to thermal properties of aggregate and concrete, due to alkali/aggregate reaction, due to sulphate action etc. Presently we shall discuss the volume change on account of inherenet properties of concrete “shrinkage”.

 

One of the most objectionable defects in concrete is the presence of cracks, particularly in floors and pavements. One of the important factors that contribute to the cracks in floors and pavements is that due to shrinkage. It is difficult to make concrete which does not shrink and crack. It is only a question of magnitude. Now the question is how to reduce the shrinkage and shrinkage cracks in concrete structures. The term shrinkage is loosely used to describe the various aspects of volume changes in concrete due to loss of moisture at different stages due to different reasons.

 

To understand this aspect more closely, shrinkage can be classified in the following way:

 

(a) Plastic Shrinkage

 

( Drying Shrinkage

 

© Autogeneous Shrinkage

 

(d) Carbonation Shrinkage

 

The Types of shrinkage are explained as below:

a. Plastic Shrinkage

 

Shrinkage of this type manifests itself soon after the concrete is placed in the forms while the concrete is still in the plastic state. Loss of water by evaporation from the surface of concrete or by the absorption by aggregate or subgrade, is believed to be the reasons of plastic shrinkage. The loss of water results in the reduction of volume. The aggregate particles or the reinforcement

comes in the way of subsidence due to which cracks may appear at the surface or internally around the aggregate or reinforcement.

In case of floors and pavements where the surface area exposed to drying is large as compared to depth, when this large surface is exposed to hot sun and drying wind, the surface of concrete dries very fast which results in plastic shrinkage. Sometimes even if the concrete is not subjected to severe drying, but poorly made with a high water/cement ratio, large quantity of water bleeds and accumulates at the surface. When this water at the surface dries out, the surface concrete collapses causing cracks.

 

Plastic concrete is sometimes subjected to unintended vibration or yielding of formwork support which again causes plastic shrinkage cracks as the concrete at this stage has not developed enough strength. From the above it can be inferred that high water/cement ratio, badly proportioned concrete, rapid drying, greater bleeding, unintended vibration etc., are some of the reasons for plastic shrinkage. It can also be further added that richer concrete undergoes greater plastic shrinkage.

 

Plastic shrinkage can be reduced mainly by preventing the rapid loss of water from surface. This can be done by covering the surface with polyethylene sheeting immediately on finishing operation; by fog spray that keeps the surface moist; or by working at night. Use of small quantity of aluminium powder is also suggested to offset the effect of plastic shrinkage.

 

Similarly, expansive cement or shrinkage compensating cement also can be used for controlling the shrinkage during the setting of concrete.

 

b. Drying Shrinkage

 

Just as the hydration of cement is an ever lasting process, the drying shrinkage is also an ever lasting process when concrete is subjected to drying conditions. The drying shrinkage of concrete is analogous to the mechanism of drying of timber specimen. The loss of free water contained in hardened concrete, does not result in any appreciable dimension change. It is the loss of water held in gel pores that causes the change in the volume. Under drying conditions, the gel water is lost progressively over a long time, as long as the concrete is kept in drying conditions. Cement paste shrinks more than mortar and mortar shrinks more than concrete. Concrete made with smaller size aggregate shrinks more than concrete made with bigger size aggregate. The magnitude of drying shrinkage is also a function of the fineness of gel. The finer the gel the more is the shrinkage.

c. Autogeneous Shrinkage

 

In a conservative system i.e. where no moisture movement to or from the paste is permitted, when temperature is constant some shrinkage may occur. The shrinkage of such a conservative system is known as autogeneous shrinkage.Autogeneous shrinkage is of minor importance and is not applicable in practice to many situations except that of mass of concrete in the interior of a concrete dam.

d. Carbonation Shrinkage

 

Carbon dioxide present in the atmosphere reacts in the presence of water with hydrated cement.

 

Calcium hydroxide [Ca(OH)2] gets converted to calcium carbonate and also some other cement compounds are decomposed. Such a complete decomposition of calcium compound in hydrated cement is chemically possible even at the low pressure of carbon dioxide in normal atmosphere. Carbonation penetrates beyond the exposed surface of concrete very slowly.

 

The rate of penetration of carbon dioxide depends also on the moisture content of the concrete and the relative humidity of the ambient medium. Carbonation is accompanied by an increase in weight of the concrete and by shrinkage.

 

Carbonation shrinkage is probably caused by the dissolution of crystals of calcium hydroxide and deposition of calcium carbonate in its place. As the new product is less in volume than the product replaced, shrinkage takes place.

 

Carbonation of concrete also results in increased strength and reduced permeability, possibly because water released by carbonation promotes the process of hydration and also calcium carbonate reduces the voids within the cement paste. As the magnitude of carbonation shrinkage is very small when compared to long term drying shrinkage, this aspect is not of much significance

 

One of the most important factors that affects shrinkage is the drying condition or in other words, the relative humidity of the atmosphere at which the concrete specimen is kept. If the concrete is placed in 100 per cent relative humidity for any length of time, there will not be any shrinkage; instead there will be a slight swelling. The typical relationship between shrinkage and time for which concrete is stored at different relative humidities is shown in Figure. The graph shows that the magnitude of shrinkage increases with time and also with the reduction of relative humidity.

 

The rate of shrinkage decreases rapidly with time. It is observed that 14 to 34 per cent of the 20 year shrinkage occurs in 2 weeks, 40 to 80 per cent of the 20 year shrinkage occurs in 3 months and 66 to 85 per cent of the 20 year shrinkage occurs in one year. Another important factor which influences the magnitude of shrinkage is water/cement ratio of the concrete. The richness of the concrete also has a significant influence on shrinkage. Aggregate plays an important role in the shrinkage properties of concrete. The quantum of an aggregate, its size, and its modulus of elasticity influence the magnitude of drying shrinkage.

 

Harder aggregate with higher modulus of elasticity like quartz shrinks much less than softer aggregates such as sandstone.

Moisture Movement Concrete shrinks when allowed to dry in air at a lower relative humidity and it swells when kept at 100 per cent relative humidity or when placed in water.

 

Just as drying shrinkage is an ever continuing process, swelling, when continuously placed in water is also an ever continuing process. If a concrete sample subjected to drying condition, at some stage, is subjected to wetting condition, it starts swelling. It is interesting to note that all the initial drying shrinkage is not recovered even after prolonged storage in water which shows that the phenomenon of drying shrinkage is not a fully reversible one.

 

Just as the drying shrinkage is due to loss of adsorbed water around gel particles, swelling is due to the adsorption of water by the cement gel. The water molecules act against the cohesive force and tend to force the gel particles further apart as a result of which swelling takes place. In addition, the ingress of water decreases the surface tension of the gel.

[Ροδοπουλος]

Εργαστηριο Ποιοτητας Σκυροδεματος

 

EXPERIMENT # 3

 

To find organic impurities in sand

 

Significance:

This test is used to determine the presence of injurious organic impurities in fine aggregates that are to be used in hydraulic cement mortar or concrete by using a strandard color solution.

 

Apparatus:

Colorless glass bottles having graduation marks at three points as follows

Standard color solution level – 75ml

Fine aggregate level – 130 ml

NaOH solution level - 200ml

 

Reagent and standard color solution:

Reagent NaOH Solution: Dissolve 3 parts by mass of sodium hydroxide in 97 parts of water

Standard Color Solution: Dissolve potassium dichromate (K2Cr2O7) in concentrated sulphuric acid at the rate of 0.25g/100ml of acid.

 

Procedure:

Take 450g of sand. Fill the glass bottle upto 130ml with sand. Add sodium hyroxide solution until volume of sand and liquid is approximately 200ml. Stopper the bottle, shake vigorously, and then allow the solution to stand for 24 hours. After 24 hours fill a glass bottle to approximately 75 ml level with fresh standard color solution. Hold the bottle with test sample and the bottle with standard color solution side by side and compare the color of the solutions. Record whether the color of the test sample is lighter, darker or equal to the color of standard color solution. If the color of test sample is darker than standard color solution then the fine aggregate under test contains injurious organic impurities.

 

 

EXPERIMENT # 4

 

Standard Test Method for Density, Specific Gravity and Absorption of Fine Aggregate

 

Theory:

Four moisture conditions are defined for aggregates depending on the amount of water held in the pores or on their surface.

 

Damp or wet:

Aggregate in which the pores are filled with water and with free water also on their surface.

 

Saturated surface dry:

Aggregate in which the pores are filled with water but with no free water on the surface.

 

Air dry:

Aggregate that has a dry surface but contains some water in the pores.

 

Oven dry:

Aggregate that contains no water in the pores or on the surface.

 

Density:

Density of material is defined as mass per unit volume. Density of water is 1000kg/m3, 1g/cc or 62.4lb/ft3.

 

Significance of density:

If a minimum density is specified, for example, in heavy weight concrete for nuclear radiation shielding and the aggregates used in concrete have density less than the specified value then the concrete used for nuclear radiation shielding will not be able to absorb nuclear radiations and it will not fulfill its purpose.

 

Specific Gravity:

The specific gravity of an aggregate is the mass of the aggregate in air divided by the mass of an equal volume of water.

 

Specific Gravity (oven dry):

Specific gravity (oven dry) of an aggregate is the oven dry mass divided by the mass of a volume of water equal to the saturated surface dry aggregate volume.

 

Specific Gravity (saturated surface dry):

Specific gravity (saturated surface dry) of an aggregate is the saturated surface dry mass divided by the mass of a volume of water equal to the saturated surface dry aggregate volume.

 

 

 

Specific Gravity (apparent):

Specific gravity (apparent) of an aggregate is the oven dry mass divided by the mass of a volume of water equal to that of the solid including the impermeable pores.

 

Significance of Specific Gravity:

The specific gravity of an aggregate is used in mixture proportioning calculations to find the absolute volume that a given mass of material will occupy in the mixture. Absolute volume of an aggregate is the volume of solid matter and internal pores excluding the spaces between the particles. The absolute volume is used to calculate the volume of a batch of concrete.

In a given concrete mixture, substituting one aggregate with another of a different specific gravity will cause the volume of concrete to change for the same batch mass. Because concrete is often sold by volume, this change means that either the purchaser is receiving less concrete than ordered or the producer is supplying more concrete than purchased.

Specific gravity can also indicate possible material contamination. Deleterious particle are often lighter than aggregate particles and therefore a large amount of deleterious material in an aggregate sample may result in a abnormally low specific gravity.

 

Absorption:

The increase in mass of aggregate due to water penetration into the pores of the particles is called absorption.

 

Significance of Absorption:

To calculate the amount of mixing water in a concrete batch, it is necessary to know the amount of water absorbed by the aggregates. If absorption value is not known then the total water needed for concrete cannot be determined accurately.

 

Apparatus:

Balance, Graduated cylinder, Oven

 

Procedure:

Partially fill the graduated cylinder with water. Add 500g of saturated surface dry (SSD) fine aggregate in graduated cylinder. Agitate the graduated cylinder to eliminate all air bubbles. After eliminating air bubbles bring the water level in graduated cylinder to its calibrated capacity. Determine the total mass of the graduated cylinder, specimen and water. Remove the fine aggregate from the graduated cylinder, dry in the oven at a temperature of 110 degree centigrade, allow to cool in air at room temperature for 1 hour and determine its mass.

Then fill the graduated cylinder to its calibrated capacity with water and determine its mass.

 

Specific gravity (oven dry) = A/ (B + S – C)

 

Specific gravity (saturated surface dry) = S/(B+S – C)

 

Specific gravity (apparent) = A/ (B+A-C)

 

Absorption % = (S-A)/A x 100

 

Where

S = mass of saturated surface dry specimen (g)

A = mass of oven dry specimen (g)

B = mass of graduated cylinder filled with water to its calibrated mark (g)

C = mass of graduated cylinder filled with specimen and water to calibration mark (g)

 

EXPERIMENT # 5

 

Standard Test Method for Density, Specific Gravity and Absorption of coarse aggregate

 

Apparatus:

Balance, Sample container, Water tank, Sieves, Oven

 

Procedure:

Dry the test sample in the oven to constant mass at a temperature of 110 degree centigrade and then cool it in air at room temperature for 1 to 3 h or until the aggregate has reached a temperature that is comfortable to handle. Immerse the coarse aggregate in water for 24 hours. Remove the test sample from water and roll it in a large absorbent cloth to remove water from surface. Determine the mass of the test sample in saturated surface dry condition. After determining the mass place the saturated surface dry sample in sample container and determine its apparent mass in water. Remove all entrapped air before determining its mass by shaking the container while immersed. Dry the test sample in oven at temperature of 110 degree centigrade, cool in air at room for 1 to 3 hours or until the aggregate is comfortable to handle and determine its mass.

 

Specific gravity (oven dry) = A/(B-C)

 

Specific gravity (saturated surface dry) = B/(B-C)

 

Specific gravity (apparent) = A/(A-C)

 

Absorption % = (B-A)/B x 100

 

Where

A= mass of oven dry test sample in air (g)

B= mass of saturated surface dry test sample in air (g)

C= apparent mass of saturated test sample in water (g)

[Ροδοπουλος]

Εργαστηριο Ποιοτητας Σκυροδεματος 2

 

PRACTICAL # 6

 

Standard Test Method for time of setting of Hydraulic cement by Vicat Needle

 

Theory:

• Hydraulic cement refers to a material which hardens under water.

 

• Portland cement is obtained by mixing together limestone, silica, alumina and iron oxide bearing materials, burning them at a clinkering temperature and grinding the resulting clinker.

 

• Four compounds are regarded as the major constituents of cement

 

Name of compound Oxide composition Abbrevation

Tricalcium silicate 3CaO.SiO2 C3S

Dicalcium silicate 2CaO.SiO2 C2S

Tricalcium aluminate 3CaO.Al2O3 C3A

Tetracalcium alumino ferrite 4CaO.Al2O3.Fe2O3 C4AF

 

• When water is added to cement, hydration of cement takes place. In the presence of water, the silicates and aluminates of Portland cement form hydrates which produce hardened cement paste. The hydration of C3S produces calcium silicate hydrate (C3S2H3) and calcium hydroxide Ca(OH)2. C2S behaves similarly but produces less lime.

 

• The hydration of cement compounds is exothermic, and the quantity of heat per gram of unhydrated cement, evolved upon complete hydration at a given temperature, is defined as the heat of hydration. For Portland cements, about one half of the total heat is liberated between 1 and 3 days, about three- quarters in 7 days and nearly 90% in 6 months. The heat of hydration depends on the chemical composition of the cement and is approximately equal to the sum of the heats of hydration of the individual pure compounds when their respective proportions by mass are hydrated separately, typical values are given in table

 

Compound Heat of hydration ( J/g)

C3S 502

C2S 260

C3A 867

C4AF 419

 

The table shows that by reducing the proportions of C3A and C3S, the heat of

hydration of cement can be reduced.

 

• Setting refers to a change from a fluid to a rigid state. Setting is mainly caused by a selective hydration of C3A and C3S and is accompanied by temperature rises in the cement paste. Setting time is the term used to describe the stiffening of cement

paste.

 

• Initial set corresponds to rapid rise and final set corresponds to the peak temperature. According to ASTM Standards initial setting time of ordinary Portland cement is 1 hour and final setting time of ordinary Portland cement is as maximum as 10 hours.

 

• Initial and final sets should be distinguished from false set which sometimes occurs within few minutes of mixing with water. No heat is evolved in a false set and the concrete can be remixed without adding water.

 

• Flash set:

The reaction of pure C3A with water is very rapid and would lead to a flash set, which is prevented by the addition of gypsum to the cement clinker.

 

• Difference b/w setting and hardening:

When cement is mixed with water to form a soft paste, it gradually stiffens until it becomes solid. This process is known as setting and hardening. The cement is said to have set when it has gained sufficient rigidity to support an arbitrarily defined pressure, after which it continues for a long time to harden i.e. to gain further strength.

 

Apparatus:

Vicat Apparatus, Balance, Plane non-absorptive plate, Flat trowel, Conical ring

 

Procedure:

Take 650 g of cement and make cement paste of standard consistence by mixing water between 26 to 33 % by mass of dry cement. Form the cement paste into a ball and toss six times from one hand to other, maintaining the hands about 6in apart. Press the ball, resting in the palm of the hand, into the larger end of the conical ring, held in the other hand, completely filling the ring with paste. Remove the excess at the larger end by a single movement of the palm of the hand. Place the ring on its larger end onto the non-absorptive plate and slice off the excess paste at the smaller end at the top of the ring with the help of flat trowel. First find the consistency of the cement paste. For this purpose center the paste confined in conical ring under 10 mm dia plunger. Set the movable indicator to upper zero mark of the scale, or take an initial reading and release the rod immediately. The paste shall be of normal consistency when the rod settles to a point 10mm below the original surface in 30 sec after being released. Make trial pastes with varying percentage of water until the normal consistency is obtained. Make each trial with fresh cement. After making the paste of normal consistency, find initial and final setting time of cement paste. Center the paste confined in conical ring under 1mm needle. Determine the penetration of the 1mm needle at this time and every 15 min thereafter until a penetration of 25mm or less is obtained. The time between the initial contact of cement and water and the penetration of 25mm is the initial setting time. The final setting time is recorded when the 1 mm needle does not produce any mark on the specimen surface or when the needle does not visibly sink into the

 

διαβασμα

 

http://www.getty.edu/conservation/publications/pdf_publications/torraca.pdf

 

το τυπωνεται. Ειναι must

[xaniared]

Αφου παρακολούθησα με τεραστια προσοχη την 2ωρη διάλεξη το μονο που μπορω να πω ειναι respect

[Ροδοπουλος]

Υπολογισμος επικαλύψης για παραθαλλάσια

 

σε προηγουμενο εχω δωσει την συγκεντρωση των χλωριόντων

 

τωρα στο λινκ σας δινω τις εξισωσεις

 

http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc47011/nrcc47011.pdf

 

Πατε στην εξισωση 2 βαζεται τον επιθυμητο χρόνο και λυνετε για dc.

 

Γιατι το ΕΝ δεν μου λεει τιποτα για την Ελλάδα και η συνταγη 30χιλιοστα ειναι πλασματική. Τωρα σαν μηχανικοί βαλτε και εναν συντελεστη ασφαλέιας.

 

Συμβουλες για Durability

 

Τοσο οι αρχιτεκτονες όσο και οι Πολ. μηχ. θα πρεπει να καταλαβουν οτι το Durability αποτελει κάτι που επηρεαζεται και απο τον αρχικό σχεδιασμό.

 

Πριν λοιπον σχεδιασουμε κατι θα πρεπει να εχουμε υποψη μας τις συνθηκες της περιοχής. Η αποσταση απο την θαλασσα, η συγκεντρωση διοξειδιου, υγρασια, κλπ.

 

Υπαρχουν πινακες κατα ΕΝ και αλλοι που μας λενε αναλογα με τον σχεδιασμό του φορεα την πιθανοτητα αλλα και τον τυπο ρυγματωσης.

 

Εαν ειμαστε σε περιοχή με αυξημενη συγκεντρωση διοξειδιου θα πρεπει τα κρισιμα στοιχεια να σχεδιαστούν με τετοιο τροπο ωστε να εχουμε αποπλυση απο την βροχη ενω ταυτοχρονα να βρισκονται σε σκιερό μέρος.

 

Ακουγεται δυσκολο αλλα δεν ειναι. Οι περιβαλλοντικοι σταθμοί περιέχουν πληροφορίες για την διευθυνση του ανεμου ολο των χρόνο και για την βροχοπτωση. Αρα κοιταμε τις περιοδους βροχόπτωσης και τον ανεμο και σχεδιαζουμε.

 

διαβασμα

 

Diffusion of chloride in concrete: theory and application

 

Δυσκολια του Durability

 

μετα απο 350 μηνυματα πιστευω οτι καταλαβαίνεται γιατι ειναι οντως δυσκολο να διδαχθεί ενα τετοιο μαθημα σε βάθος. Σε μεταπτυχιακό επιπεδο και κατω απο τον γενικό τιτλο Durability and Repair of Concrete Structures ειναι 8 ωρες την εβδομάδα για 9 μήνες. Τωρα επειδη ειναι δυσκολο θα πρεπει να το αγνοούμε. ΟΧΙ. Αλλα μακάρι να ειχαμε καποιον τροπο e-learning για μηχανικούς οπως το φόρουμ. Δεν έχουμε και με την κρίση ουτε στα επομενα 10 χρόνια το βλέπω.

 

Παντως θα συνεχίσω να σας δίνω πληροφοριες ελπίζοντας στον εκπαιδευτικό χαρακτήρα του φόρουμ. Καποια στιγμη οι συντονιστες θα πρεπει να ξεκιινησουν να το μαζεουν λιγο και να φτιαξουμε εναν οδηγό.

 

βεβαια συνεχιξω γιατι εχω τοσο πολλά ακομα να σας πω. Σιγα σιγα θελω να σας βαλω στον σχεδιασμό του Durability.

 

Ρωγμομετρο

 

Στις ρωγμες το μεγαλο προβλημα δεν ειναι το πλατος αλλα το βάθος. Το λεω αυτο επειδη το πλατος επηρεάζεταιν απο πολλούς παραμέτρους, όπως ο οπλισμος, επικαλυψη, θερμοκρασία, κλπ.

 

Μια επιφανειακή ρωγμη λογω ξηρανσης θα ειναι κατα 99% με μικρο βάθος 1-5 χιλιοστα. Αντιθετα μια πλαστική ρωγμη θα εχει βαθος 3-9 χιλιοστά παντα για επιγανειακό πλατος 0.1-0.5 χιλιοστά. Μια ενεργή ρωγμη εφελκυσμού απο την άλλη μπορειν να έχει μέχρι και 40 χιλιοστά βάθος χωρίς απαιρατητα νε ξεπερασει επιφανειακά τα 0.6 χιλιοστά. Ειδικοτερα εαν εχουμε σε καποιο σημειο του βαθους της ρωγμής οπλισμό. Εαν μηχανημα για τον εντοπισμό του βαθους ειναι

 

http://www.germann.org/Products/Surfer/Surfer.pdf

 

Επισκευή με gunite

 

Επειδη βλέπω το gunite να δουλευει πολύ για επισκευή με διαβρωμένο χάλυβα θα συνιστουσα τουλάχιστον τις προδιαγραφές που δίνω στην εικόνα. Ειδικότερα το 500 coulomb ειναι οριακή ποιότητα.

 

Maintenance-based design of concrete parking structures

 

στο λινκ

http://dspace.mit.edu/handle/1721.1/39274

 

καταβαστε και διαβάστε

 

Επισκευή απο φωτιά

 

Step 1 #

 

Determine what kind of repair is necessary by using a concrete rebound hammer. These hammers, designed to measure the remaining structural integrity in the concrete, employ a rubber impact system that measures the amount of elastic rebound when a rubber insert impacts the surface of the concrete. A digital rebound hammer will indicate when the level of impairment registers in the danger zone. (See Resources)

#

Step 2

 

Blast the soot from the surface of the concrete with either a dry ice mixture or sand. The least damaging removal method uses dry ice although locating the necessary equipment can be difficult. For a very small area of damage, you may use a wire brush and a solution of warm water and Tri-Sodium Phosphate (TSP), found at hardware stores.

#

Step 3

 

Consult an engineer if you are unsure about the structural integrity of the remaining concrete. If the fire was small, you may paint or apply a surface-strengthening bond after removing all of the soot. If there is extensive structural damage, a portion or all of the concrete may require demolition and re-construction.

#

Step 4

 

Apply a surface strengthening bond product to clean concrete to protect and seal it. Because extreme heat makes the concrete porous, a surface-bonding agent will protect it from moisture and eventual crumbling. Follow the manufacturer's instructions when applying a surface strengthener. (See Resources)

#

Step 5

Concrete spalling results in surface chipping.

 

Concrete spalling results in surface chipping.

 

Remove small areas of spalling and patch with concrete mortar. This repair is feasible if the concrete surface suffered slight damage with spalling but the integrity of the concrete structure is still intact. Mix concrete mortar with water as directed on the package and apply to the surface with a large flat trowel, smoothing it evenly as you go. If the concrete beneath is very dry--spray it down every three hours in the preceding 24-hour period to reduce premature drying of the mortar.

#

Step 6

 

Demolish concrete that no longer is safe and rebuild the structure. On large or especially hot fires, concrete may suffer damage that is beyond repair. In these cases, the only option is to remove the entire concrete structure.

[Ροδοπουλος]

Υπολογισμός ανοδιων

 

Παιδια το βαζω σε φωτο.

 

φωτό για επόμενες σελίδες.

 

τωρα οποιος φερει εισαγωγη την euclid κονομαει γερά. Εγω σιγουρα δεν εχω τα λεφτά.

 

φωτο συνεχεια σε λιγο θα βάλω και τα σχεδια επισκυεής για να παρετε μια ιδεα.

 

---------------------------------------------------------------------------------

 

Υπάρχει απο το 1972. Παιδια ειμαστε πολύ πίσω. Εχουμε θεωρία στην θεωρία και δεν εκπαιδευόμαστε στην τεχνολογία.

Επιτέλους ένας ακαδημαϊκός που το είπε. Κατά τα άλλα για την περίφημη ενημέρωση respect !!!

 

--------------------------------------------------------------------------------

 

Ειμαι παρανομος εαν δεν εφαρμοζω το ΕΝ 206-1?

 

Παιδια απαντηστε και θα το παρω απο κει.

[giorgosk]

Ειμαι παρανομος εαν δεν εφαρμοζω το ΕΝ 206-1?

 

Δεν νομίζω ότι έχει σχέση με κάποια παρανομία. Εκτός των προδιαγραφών και των κανονισμών...