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Quantification of the strength development in early age concrete and its resistance to plastic shrinkage crackingLiao, Wenbo 16 September 2021 (has links)
Early plastic shrinkage cracking of concrete is an important factor affecting the durability of modern concrete structures. Early cracking (within 24 hours after pouring) may become a problem for any concrete structure. It will promote the entry of harmful materials, destroy the beauty of concrete members, and reduce their durability and performance. In addition, due to long-term shrinkage and/or load, these cracks may gradually expand in the service life of components. Scientific research and engineering technicians often have to face the difficulties caused by early plastic shrinkage cracking of concrete.
From the aspects of shrinkage mechanism, measurement method, prediction model and strength development, this paper reviews the scientific and technological status of plastic shrinkage and strength development of early-age concrete, and based on this, summarizes the important conclusions in existing research and establishes the relevant concrete strength prediction model.:1 Introduction
2. Shrinkage in concrete
2.1 Classification and mechanism of concrete shrinkage
2.2 Main factors causing concrete shrinkage
2.3 Concluding remarks
3. Plastic shrinkage in early age concrete
3.1 Method for determining the time of initial and final setting
3.2 Mechanism of plastic shrinkage
3.3 Evaporation
3.4 Capillary pressure
3.5 Main factors affecting plastic shrinkage cracking
3.6 Concluding remarks
4. Different methods for determining the resistance to plastic shrinkage cracking
4.1 Rectangular mould test setup
4.2 ASTM C 1579
4.3 Ring test method (NT BUILD 433)
4.4 Capillary pressure test
5. Development of early age strength of concrete
5.1 Mechanical properties
5.1.1 Compressive strength
5.1.2 Tensile strength
5.1.3 Early-age shrinkage of concrete
5.2 Test and prediction model evaluation
6. Test and quantitative model
6.1 pullout tests on early-age concrete
6.1.1 Tests principle
6.1.2 test result
6.2 Compilation of existing pullout capacity prediction models
6.2.1 Strength and pullout force model based on 𝒉𝒆𝒇
6.2.2 Strength and pullout force model based on 𝒉𝒆𝒇 and ∅𝒉
6.2.3 Tensile strength and pullout force model
6.3 Application of existing prediction model in early age concrete
7. Conclusions
8. Literature
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Plastic shrinkage properties of baler twine fibre reinforced concreteChen, Ying 05 June 2008
The large amount of used polypropylene baler twine generated from the agricultural community may provide a low-cost, environmentally friendly source of fibre reinforcement that can be used to improve the properties of concrete. However, the performance of such fibres for the application has not yet been explored. The effectiveness of using small amounts of chopped baler twine to control the restrained plastic shrinkage cracking of portland cement mortar was investigated in this study. To determine the influence of baler twine fibre type, length and volume fraction on their performance, two types of baler twine ( one composed of strands with circular cross section, the other composed of flat band shape strands) in two lengths (19 mm and 38 mm) and three volume fractions (0.05%, 0.1%, and 0.3%) were evaluated. To compare the performance of baler twine fibre with that of other commercially available synthetic fibres, fibrillated polypropylene fibres at equal lengths and volume fractions was investigated.<p>The restrained plastic shrinkage tests were carried out by subjecting the fibre-reinforced mortar specimens, cast on rough substrate bases, to a wind speed of 2.6 m/s, and relative humidity less than 3% at 35 °C for 22 hours. To evaluate the effectiveness of the fibres, the crack numbers were recorded, and the maximum crack width and total crack area on the surface of each specimen were measured using an image analysis technique. Unrestrained plastic shrinkage tests were also conducted in which fibre-reinforced mortar specimens without the substrate bases were tested under the same environmental conditions.<p>Test results indicate that both types of baler twine are capable of controlling restrained plastic shrinkage cracking to some extent, but are not as effective as fibrillated polypropylene. The baler twine composed of band shape strands performed better than the one composed of strands with circular cross section. Compared with plain specimens, the total crack area was reduced by 95.3, 77.5 and 38.7% when 0.3% volume fraction of 38 mm fibrillated polypropylene, band shape baler twine and circular baler twine fibres, respectively, were added. Similar reductions in maximum crack width were observed. Fibre length did not significantly influence cracking behaviour. Free plastic shrinkage was significantly reduced only when long fibre lengths (38 mm) and high volume fractions (0.3%) were used.
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Plastic shrinkage properties of baler twine fibre reinforced concreteChen, Ying 05 June 2008 (has links)
The large amount of used polypropylene baler twine generated from the agricultural community may provide a low-cost, environmentally friendly source of fibre reinforcement that can be used to improve the properties of concrete. However, the performance of such fibres for the application has not yet been explored. The effectiveness of using small amounts of chopped baler twine to control the restrained plastic shrinkage cracking of portland cement mortar was investigated in this study. To determine the influence of baler twine fibre type, length and volume fraction on their performance, two types of baler twine ( one composed of strands with circular cross section, the other composed of flat band shape strands) in two lengths (19 mm and 38 mm) and three volume fractions (0.05%, 0.1%, and 0.3%) were evaluated. To compare the performance of baler twine fibre with that of other commercially available synthetic fibres, fibrillated polypropylene fibres at equal lengths and volume fractions was investigated.<p>The restrained plastic shrinkage tests were carried out by subjecting the fibre-reinforced mortar specimens, cast on rough substrate bases, to a wind speed of 2.6 m/s, and relative humidity less than 3% at 35 °C for 22 hours. To evaluate the effectiveness of the fibres, the crack numbers were recorded, and the maximum crack width and total crack area on the surface of each specimen were measured using an image analysis technique. Unrestrained plastic shrinkage tests were also conducted in which fibre-reinforced mortar specimens without the substrate bases were tested under the same environmental conditions.<p>Test results indicate that both types of baler twine are capable of controlling restrained plastic shrinkage cracking to some extent, but are not as effective as fibrillated polypropylene. The baler twine composed of band shape strands performed better than the one composed of strands with circular cross section. Compared with plain specimens, the total crack area was reduced by 95.3, 77.5 and 38.7% when 0.3% volume fraction of 38 mm fibrillated polypropylene, band shape baler twine and circular baler twine fibres, respectively, were added. Similar reductions in maximum crack width were observed. Fibre length did not significantly influence cracking behaviour. Free plastic shrinkage was significantly reduced only when long fibre lengths (38 mm) and high volume fractions (0.3%) were used.
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Control de la retracción plástica mediante el uso de dosificaciones de microfibras sintéticas DRYMIX y Fibra Ultrafina utilizando paneles normados / Plastic shrinkage control by the use synthetic microfibers dosages Drymix and Fibra Ultrafina using standardized panelsLlanos Falcon, Jeremy Andre, Mellado Teves, Meliza Sumak 24 July 2020 (has links)
La presente investigación buscara la dosificación optima de microfibra para controlar la retracción plástica comparando microfibras sintéticas de polipropileno FIBRA ULTRAFINA de la marca CHEMA y microfibra sintética acrílica DRYMIX RC4020 de la marca SUDAMERICANA DE FIBRAS, considerando las dosificaciones que recomiendan los proveedores por cada metro cubico de concreto. Se realizarán ensayos de laboratorio en 17 mezclas para luego medir la retracción plástica en cada una de ellas utilizando los paneles normados por el ASTM C1579-13, midiendo también las demás propiedades que serán comparadas con el desempeño de un concreto convencional.
El resultado de esta investigación será el valor de dosificación óptima con la que se logre disminuir la retracción plástica sin afectar otras propiedades del concreto, tales como resistencia a la compresión, tracción, flexión y trabajabilidad. De igual manera se realizará un análisis económico de acuerdo con las dosificaciones realizadas de las fibras anteriormente mencionadas. / The present investigation will search the optimal dosage from microfiber to control the plastic shrinkage comparing the polypropylene synthetic microfiber Fibra Ultrafina by the brand CHEMA and the acrylic synthetic microfiber Drymix RC4020 by the brand SUDAMERICANA DE FIBRAS, considering the dosages per cubic meter that the providers recommend. It will perform laboratory tests in 17 mixes by then measure the plastic shrinkage in each of them using the standardized panels by the ASTM C1579-13, also will measure the other properties that will be compared with the performance from a conventional concrete.
The investigation result will be the optimal dosage valor that can reduce the plastic shrinkage without affecting the other concrete properties like the compressive strength, tensile strength, flexural strength and slump. Likewise, it will perform an economic analysis according the fiber dosages aforementioned. / Tesis
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Propuesta de aplicación del método de auto-curado adicionando ladrillo triturado al agregado grueso para disminuir las fisuras superficiales y aumentar la resistencia a la compresión del concreto en zonas cálidas (Lima Norte) / Proposal for the application of the self-curing method by adding crushed brick to the coarse aggregate to reduce surface cracks and increase the compressive strength of concrete in warm areas (North Lima)Pinchi Morey, Sanddy Rocío, Ramirez Mejia, Hosvick Jeffer 17 February 2020 (has links)
El concreto es uno de los materiales más utilizados en el mundo de la construcción, de las cuales cada material en la mezcla depende de la resistencia que se requiera de acuerdo al análisis estructural. Dentro del proceso de producción de concreto debemos garantizar que el cemento reaccione químicamente y desarrolle la resistencia para la cual fue diseñada, para esto es importante mantenerlo hidratado en ese tiempo mediante el proceso de curado. Una técnica aún no tan conocida es el auto-curado del concreto, por lo cual es una necesidad saber cuál es su influencia en el desarrollo de la resistencia y en la disminución del porcentaje de agrietamiento del concreto en estado plástico.
El objetivo de esta tesis es determinar la influencia que tiene el reemplazar un cierto porcentaje de ladrillo triturado como reemplazo del agregado grueso; evaluando la resistencia a la compresión, resistencia a la flexión, y el agrietamiento por contracción plástica del concreto. Se desarrolló con 3 diferentes porcentajes de reemplazo de ladrillo triturado que son: 15%, 21%, 27% del peso del agregado grueso para la resistencia a la compresión (f’c) de 280 kg/cm2.
Se concluyó que reemplazo del agregado grueso por ladrillo triturado es efectivo cuando es usado hasta un máximo de 21%. Los resultados obtenidos son óptimos y viables en el tiempo, mostrándonos un aumento en la resistencia a la compresión, resistencia a la flexión y la disminución del porcentaje de fisuras en estado plástico. / Concrete is one of the most used materials in the world of construction, of which each material in the mixture depends on the strength required according to the structural analysis. Within the concrete production process, we must ensure that the cement reacts chemically and develops the resistance for which it was designed, for this it is important to keep it hydrated at that time through the curing process. A technique not yet so well known is the self-curing of concrete, so it is a necessity to know what its influence is in the development of resistance and in the reduction of the percentage of cracking of concrete in the plastic state.
The objective of this thesis is to determine the influence of replacing a certain percentage of crushed brick as a replacement for coarse aggregate; evaluating the compressive strength, flexural strength, and cracking by plastic shrinkage of concrete. It was developed with 3 different percentages of crushed brick replacement that are: 15%, 21%, 27% of the weight of the coarse aggregate for the compressive strength (f’c) of 280 kg / cm2.
It was concluded that replacement of coarse aggregate with crushed brick is effective when used up to a maximum of 21%. The results obtained are optimal and viable over time, showing an increase in compressive strength, flexural strength and a decrease in the percentage of cracks in the plastic state. / Tesis
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Plastic shrinkage cracking in conventional and low volume fibre reinforced concreteCombrinck, Riaan 12 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete
within the first few hours after the concrete has been cast. It results in unsightly surface
cracks that serve as pathways whereby corroding agents can penetrate the concrete which
shortens the expected service life of a structure. PSC is primarily a problem at large exposed
concrete surfaces for example bridge decks and slabs placed in environmental conditions
with high evaporation rates.
Most precautionary measures for PSC are externally applied and aimed to reduce the
water loss through evaporation. The addition of a low dosage of polymeric fibres to
conventional concrete is an internal preventative measure which has been shown to reduce
PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced
concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance
leads to neglect and ineffective use of preventative measures. The objective of this study is
to provide the fundamental understanding of the phenomena of PSC. To achieve the
objective, an in depth background study and experiments were conducted on fresh
conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up
between the particles of the concrete is the source of shrinkage. 2→ Air entry into a
concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and
LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and
once air entry has occurred. The critical period where the majority of the PSC occurs is
between the initial and final set of concrete. Any preventative measure for PSC is most
effective during this period. The bleeding characteristics of a mix have a significant influence
on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added
resistance that fibres give to crack widening, which increases significantly from the start of
the critical period.
The fundamental knowledge gained from this study can be utilized to develop a
practical model for the design and prevention of PSC in conventional concrete and LV-FRC. / AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton
binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak
krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die
dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot
blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat
kondisies met hoë verdamping tempo’s.
Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water
verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn
interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten
opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die
vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van
voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen
van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente
uitgevoer op gewone beton en LV-VVB.
Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die
beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→
Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is
slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug
die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is
tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees
effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige
effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die
PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die
weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode.
Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die
ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en
LV-VVB.
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[en] SHRINKAGE, CREEP AND FRACTURE OF CEMENTITIOUS COMPOSITES REINFORCED WITH BAMBOO PULP / [pt] RETRAÇÃO, FLUÊNCIA E FRATURA EM COMPÓSITOS CIMENTÍCIOS REFORÇADOS COM POLPA DE BAMBUANGELA TERESA COSTA SALES 12 July 2006 (has links)
[pt] A aplicação de compósitos cimentícios usando fibras
vegetais, em
substituição a fibras de asbestos, é uma realidade em
indústrias de fibrocimento
em vários países do mundo, pois, apesar das boas
propriedades mecânicas e
durabilidade, a utilização de asbestos acarreta problemas
de insalubridade. Fibras
vegetais, pela disponibilidade e adequação à preservação
ambiental, apresentam
vantagens sobre fibras sintéticas. O bambu é excelente
fornecedor de fibras, pelo
rápido crescimento, baixo custo e qualidade das fibras.
Usando-se a polpa do
vegetal, pode-se inserir maiores teores de fibras que,
distribuídas aleatoriamente,
conferem características isotrópicas ao compósito. Estudos
são realizados, visando
melhorar o desempenho dos compósitos com fibras vegetais.
Retração e fluência
se constituem em formas de deformação ao longo do tempo
que podem
comprometer o desempenho e reduzir a durabilidade do
material. Tratando-se de
materiais heterogêneos e sujeitos à presença de falhas, em
diversos níveis, a
aplicação da mecânica da fratura pode tornar-se valiosa
ferramenta para projeto e
controle da integridade desses compósitos, sendo a
inibição da iniciação e
propagação de trincas uma das principais funções do
reforço de fibras curtas. Esse
trabalho buscou analisar o comportamento de compósitos
cimentícios reforçados
com polpa de bambu, quanto à retração e à fluência, e
obter parâmetros que
descrevessem seu modo de fratura. Enquanto a capacidade de
sofrer retração
plástica foi reduzida, a retração livre na secagem cresceu
com o aumento do teor
de polpa de bambu no compósito, chegando a 40% de
incremento para 14% de
polpa, após um ano. Sob retração restringida, resultados
mostraram melhor
desempenho dos compósitos com fibras, pela ausência de
fissuras detectáveis por
fissurômetro, em relação à matriz sem reforço, que
apresentou fissura em torno de
4 horas de exposição à secagem. Estudo da reversibilidade
da retração mostrou
que para os compósitos predominam as deformações de
contração. Houve
aumento da fluência sob compressão simples, com a inserção
do reforço fibroso
na mistura. Na fluência sob flexão, houve aumento da
fluência específica na face comprimida com o aumento do
teor de polpa na mistura. A fluência específica sob
tração na flexão resultou maior para a matriz sem reforço
do que para os
compósitos com polpa de bambu. No estudo sobre mecânica da
fratura, os corposde-
prova entalhados de compósito com polpa apresentaram
melhoria considerável
no comportamento à flexão em relação à matriz sem reforço.
Os compósitos com
polpa mostraram-se menos sensíveis ao entalhe, com o
incremento do teor de
reforço fibroso. Observou-se considerável amolecimento
(softening) precedendo a
ruptura devido à propagação da trinca, nos compósitos. As
curvas de resistência
(curvas-R) permitiram identificar os valores de KIR que,
nos compósitos, mostrou
manter certa constância, com o aumento do comprimento da
trinca. Nesse platô da
curva, os valores médios para KIR foram de 1,88 MPa.m1/2 e
1,84 MPa.m1/2,
respectivamente, para compósitos com 8% e 14% de polpa de
bambu. Nos
compósitos, os perfis dos caminhos trilhados pelas trincas
no crescimento foram
tortuosos, sendo o mecanismo de fratura mais intensamente
dominado pela
presença do entalhe inicial na matriz sem reforço que nos
compósitos. / [en] The application of cimentitious composites using vegetal
fibers in substitution of
asbestos is a worldwide fact in the fiber cement industry.
Despite their good
mechanical properties and durability, the use of asbestos
fibers causes well-known
health hazards. Although vegetal fibers have relatively
poor mechanical properties
compared with synthetic fibers, they have other advantages
such as low cost and
low energy demand during manufacture. Bamboo is an
excellent fiber supplier,
due to its fast growth and the quality of its fibers.
Using vegetal pulp it is possible
to insert considerable amounts of fiber in a cement
matrix, which randomly
distributed confer isotropic characteristics to the
composite. Studies are carried
out aiming to improve the performance of composites with
vegetal fibers.
Shrinkage and creep are sorts of time depending
deformation that may
significantly reduce the durability and performance of the
cement based
composite. Cementitious composites are essentially
heterogeneous materials
subject to the presence of flaws at different levels due
to the presence of many
internal microcraks in the material prior to loading.
Therefore, the application of
fracture mechanics could become a suitable tool for the
design and control of the
integrity of these composites, since the inhibition of
crack initiation and
propagation is one of the main functions of the short
fiber reinforcement. This
work sought to analyze the behavior of cimentitious
composites reinforced with
bamboo pulp under shrinkage and creep and to provide
sufficient fracture
parameters to describe the failure mode of the material.
The results show that,
whereas the plastic shrinkage reduces, the free drying
shrinkage increases
proportionally to bamboo pulp content in the composite,
reaching a 40%
increment for a 14% pulp content, after one year. Under
restrained shrinkage, the
composite with bamboo pulp presents better performance
than unreinforced
matrix. Namely, under same boundary conditions, while the
unreinforced matrix
presents cracks after about four hours, the composites
present no cracks visible through a 10x magnifying glass,
even after forty five days of drying. Study of the
shrinkage reversibility of the composite showed that there
is contraction
deformation prevalence. Under simple compression, the
creep capacity of the
bamboo pulp composites increases proportionally with the
fiber content. Under
bending stress, there was an increase of the specific
creep in the compressed face
of the specimen, as the pulp content of the mixture
increases. The specific creep
under bending tension for the tensile face was greater for
the unreinforced matrix
than in the bamboo pulp composites. As revealed through
the assessment of
fracture behavior of composites with bamboo pulp, notched
specimens presented a
considerable improvement in bending behavior when compared
to the
unreinforced matrix. The composites with pulp became less
sensible to the notch
with the increment of pulp content. In the bamboo pulp
composites, considerable
softening was observed in the load-displacement curve, as
load gradually
decreases after the peak load and before the rupture due
to crack propagation.
Using resistance curves (R-curves) it was possible to
identify the KIR values that,
for the composites, kept certain constancy as the crack
length increased. At this
plateau of the curve, the average values for KIR reached
1,88 MPa.m1/2 and 1,84
MPa.m1/2 for composites with bamboo pulp content of 8% and
14% respectively.
In the composites, crack profiles and crack surfaces were
tortuous, while in the
unreinforced matrix the fracture mechanisms were more
intensely dominated by
the presence of the initial notch.
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Etude du retrait plastique des bétons à base de granulats recyclés avec mesure de l'influence de leur degré de saturation / A study on the plastic shrinkage of recycled concretes and impact assessment of the recycled aggregates degree of saturation influenceSouche, Jean-Claude 10 December 2015 (has links)
Dans une démarche de valorisation des déchets, les granulats recyclés sont introduits dans la formulation des bétons pour donner naissance à de nouveaux bétons recyclés qui représentent l’objet du projet national RECYBETON et du projet ANR ECOREB. Cette thèse se concentre sur l’étude du béton frais et en particulier la maîtrise du retrait plastique et l’effet du degré de saturation initial des gravillons recyclés sur le comportement des bétons recyclés. Deux familles de bétons avec des rapports eau/ciment respectifs de 0,6 et 0,45 ont été testés en conditions endogènes ainsi qu’en dessiccation (Vvent = 8 m/s). Chaque famille de bétons est constituée d’un béton naturel de référence et de deux bétons recyclés différenciés pas le degré initial de saturation des gravillons recyclés (50 et 120 % de l’absorption nominale). Les résultats expérimentaux soulignent la capacité des gravillons recyclés initialement partiellement saturés à capter rapidement l’eau contenue dans la pâte de ciment, modifiant ainsi le rapport E/C, les propriétés rhéologiques du béton frais et les résistances mécaniques du béton durci. Après saturation en eau, si les conditions de séchage conduisent à un manque d’eau dans le béton, les gravillons recyclés peuvent fournir de l’eau à la pâte. Ils constituent donc un potentiel de cure interne. Le retrait plastique sous vent est explicitement lié au ressuage, au développement de la pression capillaire et à la fissuration. Le temps d’initiation de la fissuration dépend de la quantité d’eau totale dans le béton et de sa capacité à ressuer tandis que l’ouverture de fissure varie avec la valeur de retrait plastique mesurée. Dans cette étude, le développement de la pression capillaire est la cause de la fissuration qui apparaît dès l’entrée d’air dans le matériau poreux. Les différences de comportements les plus importantes sont observées entre bétons ayant une quantité d’eau totale différente plutôt qu’entre bétons naturel et recyclé. La compilation des résultats expérimentaux a permis de mettre sur pied des modélisations qui illustrent les comportements observés. Les pores concernés par l’entrée d’air dans les bétons recyclés et naturels au moment de la fissuration sont les plus gros pores de la pâte. Enfin, un couplage hygrothermique séchage-température du béton peut influer sur le démarrage de l’hydratation. / In the context of sustainable development, the reuse of construction and demolition waste is necessary to conserve nonrenewable natural aggregate resources, so recycled aggregates are introduced in concrete mix design. This is the aim of the national projet RECYBETON and the research project ECOREB. This study deals with the fresh concrete and more specifically with shrinkage control and the effects of the initial saturation degrees of recycled coarse aggregates on concrete behavior.Two concrete families, with two different water/cement ratios 0,60 and 0,45, are tested under endogenous and drying (wind speed equal to 8 m/s) conditions. Each concrete family contains a reference natural concrete and two recycled concretes. The initial saturation degree is the difference between them (recycled coarse aggregates saturated or semi saturated).Experimental results underline the capacity of non-saturated aggregates to quickly absorb water from cement paste, modifying the W/C ratio, rheological properties of the fresh concrete and the mechanical strength (at 28 days) of recycled concretes. After saturation in water, recycled aggregates can release water into the cement paste if the undergone drying conditions lead to a lack of water in the cement matrix. The recycled coarse aggregates can be seen as an internal curing potential.Experimental plastic shrinkage studies carried out under drying conditions highlight a link between bleeding, capillary pressure, plastic shrinkage and cracking. It should be pointed out that the initial cracking is dependent on the total quantity of water in the concrete and on its bleeding capacity. The opening cracks vary with the plastic shrinkage values measured during the test. The analysis of the results emphasize that the capillary pressure is the determining parameter and that the air entry value matches the cracks. The major behavior differences are found between concretes with different volumes of water rather than between natural and recycled concretes.Finally, the analysis of all the experimental results have allowed concrete modelling and understanding why concretes do not behave in the same way. When it cracks, the air come in the biggest pores of the concrete paste. Moreover, a hygrothermal coupling exists between the drying and the temperature in concrete. It can affect hydration start up.
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Propuesta de concretos con cementos adicionados y fibras estructurales para mitigar la fisuración por contracción plástica y por secado en edificios de ductilidad limitada en Lima / Proposal of concrete with additional cements and structural fibers to mitigate cracking by plastic contraction and by drying in buildings of limited ductility in limaBarturén del Villar, Christian Alex, Durand Yucra, David Angel 25 February 2022 (has links)
La presente tesis contempla el diseño de una gama de concretos de baja contracción, empleando cementos con adición de puzolanas, fibras de polipropileno y fibras metálicas para mitigar la fisuración, mejorando la durabilidad de las edificaciones. Para proponer los diseños se investigó cuáles de las contracciones son la que tienen mayor incidencia en la fisuración del concreto, siendo la contracción plástica y la contracción por secado las más importantes. Asimismo, se estudiaron qué variables son las que provocan la contracción y posterior fisuramiento, afirmando que son producidos por factores ambientales, los componentes del concreto y malas prácticas constructivas.
En la primera etapa, se realizó la caracterización de los agregados (fino y grueso), realizándose ensayos como granulometría, absorción, peso específico, contenido de humedad y %pasante de la malla #200. En la segunda etapa se realizaron los ensayos en concreto fresco, siendo el de mayor importancia el ensayo de simulación de contracción plástica, para el cual empleamos la ASTM C1579. Para realizar este ensayo se fabricaron los paneles que simulan restricciones y se construyó una cámara en la que se controla la velocidad del aire, temperatura y humedad relativa. En la tercera etapa se realizaron los ensayos en concreto endurecido, siendo el más importante el ensayo de contracción por secado, para lo cual empleamos la ASTM C490. Para ello, se realizaron probetas rectangulares para la medición de la variación del cambio de longitud durante 31 días. Finalmente, se realizará el análisis costo – beneficio para demostrar la viabilidad de la propuesta. / This thesis contemplates the design of a range of low-shrinkage concretes, using cements with the addition of pozzolans, polypropylene fibers and metallic fibers to mitigate cracking, improving the durability of buildings. In order to propose the designs, it was investigated which of the contractions have the greatest incidence in the cracking of the concrete, being the plastic contraction and the drying contraction the most important. Likewise, the variables that cause contraction and subsequent cracking were studied, stating that they are produced by environmental factors, concrete components and poor construction practices.
In the first stage, the characterization of the aggregates (fine and coarse) was carried out, performing tests such as granulometry, absorption, specific weight, moisture content and% passing through of the # 200 mesh. In the second stage, tests were carried out on fresh concrete, the most important being the plastic shrinkage simulation test, for which we used ASTM C1579. To carry out this test, the panels that simulate restrictions were manufactured and a chamber was built in which the air speed, temperature and relative humidity were controlled. In the third stage, tests were carried out on hardened concrete, the most important being the drying shrinkage test, for which we used ASTM C490. For this, rectangular test tubes were made to measure the variation of the change in length during 31 days. Finally, a cost-benefit analysis will be carried out to demonstrate the viability of the proposal. / Tesis
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Evaluación comparativa de las propiedades plasticas y mecanicas del concreto F’C 210 kg/cm2 reforzado con microfibras sinteticas de polipropileno de 20 y 30mm en losas de viviendas expuestas a altas temperaturas en Ucayali / omparative evaluation of the plastic and mechanical properties of concrete f'c 210 kg / cm2 reinforced with 20 and 30mm synthetic polypropylene microfibers in housing slabs exposed to high temperatures in ucayaliCcasani Caballero, Jean Frank Aurelio, Eduardo Carrascal, Carlos Sebastian 24 May 2021 (has links)
La presente investigación se basa en el estudio de la influencia de microfibras sintéticas de polipropileno en las propiedades mecánicas y plásticas de losas de concreto f’c=210 kg/cm2 expuestas a altas temperaturas en el departamento de Ucayali. Para ello, se procedió a realizar mezclas de concreto con dos microfibras de polipropileno de 20 y 30 milímetros de longitud, a su vez, dichas mezclas fueron dosificadas con 600, 900 y 1200 g/m3 de concreto y evaluarlas respecto a contracción platica, resistencia a compresión y flexión residual. El primer ensayo, se realizó en base a la Norma ASTM C-1579 (Método de prueba estándar para evaluar el agrietamiento por contracción plástica del hormigón reforzado con fibra restringida), evaluando losas de concreto de 560x355x100 mm. sometidas a temperaturas mayores a 27°C y velocidades de viento de 8 km/h y compararlas entre la muestra patrón y muestras reforzadas con microfibras; obteniéndose una Relación de Reducción de Grietas (CRR) máxima de 68.50% para el concreto con fibra de 300 mm. y una dosificación de 1200 g/m3. Para el ensayo de compresión, guiado por la NTP 339.034 – ASTM-C39 (Método de ensayo normalizado para la determinación de la resistencia a la compresión del concreto, en muestras cilíndricas) se ensayaron probetas de 6x12 pulgadas para cada longitud de y dosificación de microfibra para compararlas respecto a la mezcla convencional; para el concreto con microfibra de 30 mm se obtuvo un incremento promedio de 8% para una dosificación de 1200 gr/m3 para un tiempo de curado de 28 días, por otro lado, la de 20 mm alcanzo incrementos máximos de 7% para la misma dosificación y tiempo de curado que el anterior. Para el último ensayo, se basó de la Norma ASTM C 1399 (Método de ensayo para determinar el esfuerzo residual promedio del concreto reforzado con fibra), en la cual se evaluaron muestras prismáticas de 100x100x350 mm sometiéndolas a cargas para obtener cual es la tensión residual que soportan a diferentes deformaciones para cada tipo de microfibras y dosificaciones. El concreto reforzado con microfibra sintética de 30 mm, obtuvo mayores valores de tensiones residuales (1.95 MPa para 1200 gr/m3) para todas las dosificaciones estudiadas en comparación a la de 20 mm. (1.86 MPa 1200 gr/m3). Al finalizar la experimentación, se concluyó que la microfibra sintética de polipropileno de 30 mm tuvo mejor desenvolvimiento que la de 20 mm para los 3 ensayos realizados. Además, se observó una relación directa entre el aumento de las propiedades mecánicas y plásticas con la cantidad de dosificación incorporada al concreto. / This research is based on the study of the influence of synthetic polypropylene microfibers on the mechanical and plastic properties of concrete slabs f’c = 210 kg / cm2 exposed to high temperatures in Ucayali. For this, concrete mixtures with two microfibers of 20 and 30 millimeters in length were made, in turn, dosages of 600, 900 and 1200 g / m3 of concrete were included and evaluated for plastic contraction, compressive strength and residual flexion. The first test was carried out on the basis of ASTM C-1579 (Standard test method to evaluate cracking by plastic contraction of reinforced fiber reinforced concrete), evaluating concrete slabs of 560x355x100 mm subjected to temperatures greater than 27 ° C and wind speeds of 8 km / h and compare them between standard samples and reinforced with microfibers; obtaining maximum Crack Reduction Ratio (CRR) of 68.50% for concrete with 300 mm fiber. and a dosage of 1200 g / m3. For the compression test, guided by Standard NTP 339.034 - ASTM-C39 (Standard test method for the determination of the compressive strength of concrete, in cylindrical samples) 6x12 inch specimens were tested for each microfiber and dosing to compare them with respect to the conventional mixture; for concrete with 30 mm microfiber an average increase of 8% was obtained for a dosage of 1200 gr / m3 for a curing time of 28 days, on the other hand, the 20 mm reached maximum increases of 7% for the same dosage and cure time than the previous one. For the last test, it was based on ASTM C 1399 (Test method to determine the average residual stress of fiber reinforced concrete), in which prismatic samples of 100x100x350 mm were evaluated by subjecting them to loads to obtain what the residual tension is that support different deformations for each type of microfibers and dosages. The reinforced concrete with synthetic microfiber of 30 mm, obtained higher values of residual stresses (1.95 MPa for 1200 gr / m3) for all the dosages studied in comparison to that of 20 mm. (1.86 MPa 1200 gr / m3). At the end of the experimentation, it was concluded that the 30 mm polypropylene synthetic microfiber had a better performance than the 20 mm microfiber for the 3 tests performed. In addition, a direct relationship was observed between the increase in mechanical and plastic properties with the amount of dosage incorporated into the concrete. / Tesis
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