Analysis of Friction and Lubrication Conditions of Concrete/Formwork Interfaces

IJSRD - International Journal for Scientific Research & Development| Vol. 4, Issue 05, 2016 | ISSN (online): 2321-0613

Analysis of Friction and Lubrication Conditions of Concrete/Formwork Interfaces Pranay Kumar Singh1 Vishal Gupta2 1 Resident Engineer 2M.Tech Scholar 1 MSV International INC 2RKDF, Bhopal Abstract— Concrete friction plays a basic role throughout numerous stages of construction and structure operations, together with pumping, formwork filling and also the production of facings. A tribometer for fluid materials has therefore been developed to higher study this friction. Tests performed with sure modifications of interface conditions show that friction is ruled by surface characteristics (e.g. kind of demoulding agent, roughness, velocity, pressure). The investigation showed that the tribometer is sensitive to get a true understanding of the mechanical behaviour of the SelfConsolidating Concrete (SCC). The tests and observations created reveal that friction mechanisms rely on the properties of the interface. The interface seems to endure 2 forms of phenomena that rely of the pressure. The demoulding oil generates a discount of the friction between the SCC and also the formwork. Parameters specific to facing look also are addressed during this paper.

Key words: SCC, Friction, Formwork, Tribometer, Aesthetics I. INTRODUCTION Since the 1980's, the employment of Self-Consolidating Concrete (SCC) has full-grown significantly in quality. several important structures of varied varieties have currently been engineered with this material. At present, all key building business actors take into consideration the progress provided by this material. SCC is additionally extremely enticing to project house owners and designers because of its end in terms of facing quality. the looks of facings constitutes one amongst the most SCC benefits. the employment of effective demoulding agents helps guarantee an ideal final product in term of aesthetic quality. whereas the oils have already been with success characterised, our understanding of the thickness of oils applied onto formwork walls before casting remains lacking. Facing quality depends totally on the concrete skin properties, i.e. the layer of fabric connected with the formwork skin. this may touch the primary tenths of millimetres of concrete, in influencing each color and texture.

Demoulding oils also are utilized by formwork makers to limit corrosion phenomena. once subjected to repeat concrete running, the oil film really disappears and wear begins to occur as aggregates have to be compelled to be enclosed within the style of formwork installations capable of withstanding the concrete pressure. Over the past few years, many researchers have begun specializing in friction at the concrete/formwork interface, as a way of either crucial the lateral pressure of concrete against the formwork or conducting phenomenological studies. 2 plane/plane tribometers are specially designed for such studies. The underlying principle is identical for each devices, i.e. a metal plate connected with a movable concrete surface. These devices square measure capable of reproducing the conditions encountered as concrete is being poured into the formwork. many researchers have projected prognostic models for

crucial the concrete pressure against formwork. Vanhove et al. and Proske et al. have developed a prognostic model supported Janssen's theory so as to judge concrete pressure against a formwork. each these models introduce a constant of friction that depends on many parameters. This paper is aimed toward finding out the influence of those parameters on the constant of friction at the concrete/wall interface and, consequently, encompasses their influence on concrete pressure against the formwork yet. The results output concern the behavioral study of a SCC used throughout the national project command at the Bhopal experimental website (France). In order to higher perceive the mechanisms going down at the concrete/wall interface, testing was conducted within the laboratory each with and while not demoulding oil. supported a series of tribometric tests, complemented by chemistry electric resistance spectrum analysis, numerous phenomenological models can be established to clarify the mechanisms in result at the concrete/oil/formwork interface.

A study specializing in facing aesthetics has additionally been conducted for the aim of distinctive a correlation between the protocol for applying demoulding oil and facing aesthetics.

II. THE TRIBOMETER The principle adopted herein is to press a sample of concrete against a moving metal surface. The plate has been cut out from formwork walls by a formwork manufacturer. The sample holders were cylinders a hundred and twenty millimetre in diameter fitted with a hatch to feed the concrete, that had been pressurised by the utilization of gas jacks. A sealer system was put in on the sample holders thus on guarantee full containment of the concrete while not damaging the oil film applied on the plate. A mobile bottom was additionally placed at the rear of the sample so as to transmit the pressure delivered (N) by the gas jack to the concrete. This device has already been delineated in several publications. For each take a look at, the tangential force (or resistance force) has been recorded consistent with time. This force corresponds to 2 separate resistance forces, namely: on the one hand, the resultant force of the interference friction force on the seal system acting against the metal plate, further because the resultant force of the tie against the slide; on the opposite hand, the resultant force of the tangential friction force of each material samples against the plate, i.e. 2F, if friction is taken into account to be similar for the 2 samples tested.

III. PROPERTIES OF MATERIALS AND OIL A. The Metal Plate: Previous studies administrated on concretes have disclosed that surface roughness exerts a big influence on the friction constant. Roughness measurements of formwork walls were recorded at the Bhopal web site employing a moveable roughness meter (Ra = one Âľm, Rt = 9 Âľm). Ra is that the

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Analysis of Friction and Lubrication Conditions of Concrete/Formwork Interfaces (IJSRD/Vol. 4/Issue 05/2016/119)

mean deviation relative to the typical line, whereas Rt is that the distance between the best most and lowest minimum on the roughness profile. For this study, a plate has been cut out from a formwork wall. Machining ridges run within the direction of plate displacement.

B. Concrete Combine Style: This study has centered on the behavior of a SCC that had been used throughout the national project administered at the Bhopal experimental web site. the chosen concrete classification is usually utilized for applied science structures; this concrete options smart physics characteristics as regards each liquidness and stability. rock additions (filler) were introduced into the composition of take a look at specimens as a method of rising facing quality in terms of color uniformity. The concrete composition and characteristics are listed in Table one. The particle size distribution analysis of the cement, filler, sand and coarse mixture has served to see the most diameter Dmax of the grains, yet because the share of grain diameters (D) capable of changing into lodged among the plate asperities. The concrete particle size distribution is incredibly wide unfold, extending from roughly a metric linear unit for cement grains up to eight millimetre for gravel diameter. The cement and filler grains with diameters smaller than ten µm can doubtless become lodged within the tribometer plate asperities. The term fine particles or just fines refers to any or all cement and filler elements whose diameter is a smaller amount than eighty µm.

Mixing was performed in accordance with the IS specification, The operational protocol enforced was as follows: C. The Oil Used: The oil chosen for this study has a plant-based composition (denoted V for vegetable). It is 95% biodegradable without requiring the use of solvents. It has been used at the Bhopal site.

D. Oil Application Protocols: Demoulding oils should be applied homogeneously over the complete wall of a formwork. Their application needs the utilization of a sprayer fitted with associate degree tailored nozzle. Any excess product is removed, as needed, with a hand tool. Literature offers a unique thickness in step with the film. so a two µm film will offers a decent quality facing, however ten µm may also offers sensible aesthetic results.

Excess oil but might result in facing defects (bubbling). The conditions for applying oils on formworks (Bhopal) were replicated within the laboratory. 2 cases were examined in detail: application of the oil by spraying employing a round shape nozzle followed or not followed by spreading with a rubber hand tool. The oil film thickness was measured by suggests that of 2 distinct methods: deliberation and a way supported ionizing radiation. A sample formwork with a dimension of 5x3 cm2 was tested for the primary technique.

In knowing the mass density of each the oil and also the plate surface, it's merely necessary to weigh the sample so as to see the oil thickness. activity uncertainty equals +/- zero.15 µm.

The oil film thickness activity principle depends on the probabilities offered by the PIXE device, furthermore as on the properties of rays, that are material particles containing 2 protons and a couple of neutrons) launched at high speed (with associate degree energy capable five.3 MeV). Oil

thickness is measured from the most visible light X of the steel composing the metal plate. the extent of steel visible light is directly influenced by attenuation of X-rays within the oil film. From the detection of emitted X protons (given that the film solely absorbs atiny low amount), the amount of particles reaching the wall (through the oil film) will be measured, in step with an easy activity protocol by metric absorption. Moreover, terribly sturdy technique sensitivity has been ascertained. Friction tests, with and while not demoulding oil, were then conducted underneath the casting conditions enforced at the experimental web site of the national project. The pressures analysed, that simulate concrete pressure against the formwork, were outlined relative to most pressures recorded at the formwork base. At the Bhopal web site, half-dozen concrete walls of five and ten m high were solid. The pressures calculated at the formwork base equalled to 118 kPa (for the five meter high wall) and 235 kPa (for the ten meter high wall). The relative slippy rate of the concrete against the tribometer plate were calculated supported the concreting speeds and ground expanse of every formwork. These speeds varied from one.57 to 12.08 mm/s.

IV. INFLUENCE OF THE CONTACT PRESSURE The variation of friction constant µ with the concrete pressure against the plate while not demoulding oil is shown in Fig. half-dozen for a speed of five mm/s. The variation during this constant isn't linear. Two zones can be distinguished, thus reflecting two distinct types of friction. This curve displays a minimum at a pressure of 150 kPa. This same trend can be observed for other concrete mix designs. This critical value is equal to 110 kPa for a conventional concrete. Despite its look, fluid concrete isn't an eternal medium. the varied concrete components can play terribly specific roles once friction happens. The pressure stress applied to the fabric is transmitted to the granular section likewise on the paste shaped by the binder (cement + filler). This pressure can then cause a little of the liquid section and fines to migrate towards the interface. A lubricating surface (or boundary) layer (water + fines) of thickness "e" is therefore shaped at the interface. by experimentation speaking, the problem of light sheared interface phenomena stems from the problem of instrumenting the materials connected and, additional specifically, the physical phenomenon. as a result of the cement particle and filler scales, Schwendenmam and Vanhove et al. used 2 techniques to develop associate understanding of this complicated interface. whether or not by suggests that of ultrasound or radiation, each strategies indicated a decrease in combination (sand and gravel) concentration close to the wall. At depression, the development at the concrete/wall interface is triggered by the onset of microstructural transcription tied to initiating concrete pressurization at the interface. The grains contained within the physical phenomenon have variety of degrees of freedom, that serves to facilitate shear. As of one hundred fifty kPa (critical pressure), a little of the physical phenomenon can migrate towards less stressed zones. supported the conclusions drawn from these 2 studies, a planned description of the mechanisms at work will be generated. The plate roughness Rt equals to nine µm, that permits the likelihood that a little of the cement and filler grains (D < ten µm) becomes lodged in surface asperities.

Shear primarily takes place during this layer. For pressures

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Analysis of Friction and Lubrication Conditions of Concrete/Formwork Interfaces (IJSRD/Vol. 4/Issue 05/2016/119)

extraordinary one hundred fifty kPa, a vicinity of the physical phenomenon will migrate towards less stressed zones. The sand or gravel grains are placed in direct contact with the asperity tips (i.e. granular friction). The force exerted by the following pointers throughout plate displacement can result in their rotation, therefore giving rise to hefty energy dissipation and leading to a quicker increase in each the friction constant and metal surface wear. once a series of tests equivalent to roughly seventy passes of concrete on the plate, the grains another each dimension and depth to the asperities.

Ra price of two µm associated an Rt of twenty six.8 µm were found.

V. INFLUENCE OF THE SLIPPY RATE The variation of the friction constant with the slippy rate for three contact pressures Below a five mm/s slippy rate, the friction constant gift a small sensitivity. on the far side this price, a stable evolution of the friction constant is determined.

Between 0.5 five|to five} mm/s, beneath the pressure result and with a sufficiently long amount, a limit layer and an area of fines components from the sand becomes lodged within the plate asperities. The cutting is found during this physical phenomenon. once the slippy rate is bigger than five mm/s, a granular friction takes place.

VI. RESULT MECHANISMS OF THE DEMOULDING OIL WITH THE APPLICATION PROTOCOL

The evolution of the friction constant with the contact pressure for each oil application protocols. a discount within the constant of friction are often determined. This decrease is a lot of pronounced for the sprayed oil. Like for friction while not oil, the crucial pressure lies at a hundred and fifty kPa no matter the oil application protocol. Beyond one hundred fifty kPa, the impact of oil minimizes granular friction. Libessart et al., in his study supposed to raised perceive oil/concrete/wall interface mechanisms, performed a series of tests on numerous parts of a specific oil combine style. This author studied the proportion of acidifier and solvent in a very plant-based oil and furthermore incontestible that the impact of a base alone depends in massive half on the thickness being applied. The physical impact takes precedence over the chemical impact. Conversely, the presence of associate degree acidifier strengthens the chemical impact by making a larger amount of soap at the interface. The oil introduced in our study consists of a vegetable base and void of any solvents. during this specific case, the oil film thickness determines friction, that explains the results.

VII. INFLUENCE OF THE DEMOULDING OIL ON THE AESTHETIC OF THE FACINGS

Few results area unit given concerning the aesthetic flaws encountered on concrete facing when formwork removal. the 2 application protocols represented on top of are analyzed.

Moulds sized thirty x thirty x thirty cm were designed by constant formwork manufacturer because the one that designed the tribometer plate. Regardless of the application protocol employed, the facings are of high quality and show very little bubbling. No concrete attachment points exist on the wall. On the opposite hand, in depth fouling and dirt accumulation are determined on the mould surface for oil scraped when spraying.

VIII. CONCLUSION This study has shown the importance of interface conditions once gushing self-compacting concretes into the formworks. to grasp the role of the demoulding agent, it's essential to realize understanding of phenomena at the concrete/oil/formwork interface. The static study of the concrete into the mould, show that the oil film of regarding zero.8 µm of thickness is ample to get a facing quality. it's been determined on web site that associate degree way over oil entailed a foul quality of the concrete facing. In dynamic, that correspond to the concrete movement against the formwork surface, the friction constant decreases by regarding half-hour. The originality of this analysis lies within the proven fact that only a few studies have antecedently been conducted during this field.

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