Pedro L Valdez | Universidad Autónoma de Nuevo León (original) (raw)

Papers by Pedro L Valdez

2008 Concrete Bridge Conference, 2008

Abstract: Corrosion of steel reinforcement is the most important durability problem in reinforced... more Abstract: Corrosion of steel reinforcement is the most important durability problem in reinforced concrete structures. Bridges are particularly susceptible to corrosion due to chlorides contained in both sea water and thawing salts, or carbonation because high ...

This research intends to identify both inexpensive and durable construction materials. Steel, gla... more This research intends to identify both inexpensive and durable construction materials. Steel, glass and polymer fibers are feasible, expensive alternatives. Natural fibers can be a real possibility for developing countries, due to the fact that these kinds of fibers are available in great quantities, while they are also renewable. Natural fiber affected mainly by the alkalinity of the cementitiuos matrix in the concrete. The durability of the composite will depend on the protection which the fiber has, and on the impermeability features of the cementitiuos matrix.

Construction and Building Materials, 2019

h i g h l i g h t s New knowledge about the substitution of OPC by fly ash(FA) and limestone fill... more h i g h l i g h t s New knowledge about the substitution of OPC by fly ash(FA) and limestone filler(LF). Appropriate combinations of FA + LF counteracts the setting delays in FA concretes. Appropriate combinations of FA+LF improve resistivity and volume stability.

Journal of Building Physics, 2010

As sustainability moves to the forefront of construction, the utilization of high-volume fly ash ... more As sustainability moves to the forefront of construction, the utilization of high-volume fly ash concrete mixtures to reduce CO2 emissions and cement consumption per unit volume of concrete placed is receiving renewed interest. Concrete mixtures in which the fly ash replaces 50% or more of the Portland cement are both economically and technically viable. This article focuses on a characterization of the thermal properties, namely, specific heat capacity and thermal conductivity, of such mixtures. Both the raw materials and the finished products (mortars and concretes) are evaluated using a transient plane source method. Because the specimens being examined are well hydrated, estimates of the specific heat capacity based on a law of mixtures, with a ‘bound water’ specific heat capacity value being employed for the water in the mixture, provide reasonable predictions of the measured performance. As with most materials, thermal conductivity is found to be a function of density, while a...

Construction and Building Materials, 2012

ABSTRACT

Revista Romana de materiale = Romanian journal of materials = RRM

ABSTRACT

This research covers the characterization of four natural pozzolan materials with igneous origin.... more This research covers the characterization of four natural pozzolan materials with igneous origin. The pozzolanic activity index of natural pozzolan-calcium hydroxide systems was determined using the compressive strength of mortar cubes. The rate of the pozzolanic reaction was determined in pastes with the same mix design that was used to make the mortars, this was achieved measuring the changes in time in the Calcium Hydroxide concentration. This information can be used as a preliminary selection tool, to evaluate the pozzolanic potential of natural pozzolan quarries.

Building and environment, 2007

The main objective of the present research was to provide the housing alternatives to istle zone ... more The main objective of the present research was to provide the housing alternatives to istle zone rural areas in Me´xico, which represent about 10% of the national territory. The proposed solution involved a sustainable portland cement-based composite material, reinforced with high tensile strength natural fibers of ''Agave lecheguilla''.

Canadian Journal of Civil Engineering, 2009

Le comportement mécanique des bétons renforcés de fibres naturelles dépend principalement de l'ad... more Le comportement mécanique des bétons renforcés de fibres naturelles dépend principalement de l'adhérence entre la fibre et la matrice de ciment. Cette adhérence a aussi une certaine influence sur le type d'endommagement de ces matériaux. Cette recherche a été menée sur des fibres naturelles de lecheguilla (Agave lecheguilla). Des essais chimiques, physiques et mécaniques tels que la détermination de la composition chimique, la morphologie, la porosité, l'absorption d'eau et les résistances à la traction et à la flexion ont été réalisés en utilisant ces fibres naturelles. Des observations à l'interface fibre-matrice de ciment ont aussi été effectuées à l'aide du stéréoscope pour évaluer l'effet du milieu alcalin et de différents rapports eau/ciment (E/C) sur la performance de mortier fibré. On a constaté que la résistance mécanique à la traction et à la flexion du matériau composite augmente, d'une part, avec l'augmentation de la longueur et, d'autre part, avec la diminution du volume de fibres utilisé. Le principal type de défaillance observée est l'arrachement des fibres. De plus, l'adhérence entre les fibres et la matrice de ciment est modifiée par les changements volumétriques et l'absorption d'eau relativement élevée. Néanmoins, cette adhérence peut être substantiellement améliorée en faisant un traitement superficiel des fibres à l'aide de solutions chimiques, comme le xylène, et en utilisant des faibles rapports E/C.

Results of interrelated tests for physical-chemical and microstructural properties of four synthe... more Results of interrelated tests for physical-chemical and microstructural properties of four synthetic pozzolanas evaluating the hydration rate in blends with calcium hydroxide are presented. The pozzolanic activity of silica fume, classified fly ash, raw fly ash and commercial metakaolin was estimated. Results showed a clear relationship between the calcium hydroxide consumption and the reactive phase content, specific surface area and porosity of the pozzolans. The calcium hydroxide-silica fume blend consumed 98% of portlandite after 21 days, whereas the system with metakaolin also presented an effective pozzolanic activity with 94% depletion. The fly ashes were the less effective pozzolans of the study.

Nanotechnology has changed our vision, expectations and abilities to control the material world. ... more Nanotechnology has changed our vision, expectations and abilities to control the material world. The developments in nano-science will have a great impact on the field of construction materials. Portland cement, one of the largest commodities consumed by mankind, is obviously the product with great, but not completely explored potential. Better understanding and engineering of complex structure of cement based materials at the nano-level will apparently result in a new generation of concrete, stronger and more durable, with desired stress-strain behavior and possibly possessing the range of newly introduced "smart" properties.

Construction and Building Materials, 2012

h i g h l i g h t s " We studied hemihydrate-slag-pozzolanas pastes with improved performance tha... more h i g h l i g h t s " We studied hemihydrate-slag-pozzolanas pastes with improved performance than plasters. " The main hydration products are gypsum, ettringite and C-S-H. " Density is slightly higher than pure plasters but strength is almost triplicate. " Silica fume additions translate in excellent dimensional stability after 180 days.

The influence of carbonation on mortars containing 25% of fly ash instead of the cementitious mat... more The influence of carbonation on mortars containing 25% of fly ash instead of the cementitious materials was studied. Mortar cylinder specimens were fabricated for 4 different W/C ratios: 0.35, 0.45, 0.55 and 0.65. Mortars with and without fly ash were subjected to an accelerated carbonation process. Volumetric weight, water absorption, compressive strength, water permeability, pH and mercury intrusion porosimetry of the mortar specimens were determined. Due to the fly ash pozzolanic potential, for all W/C ratios, results of the compressive strength tests at 28 days of the mortars with and without fly ash were similar. Mortars with fly ash presented similar water permeability as mortars without fly ash. PH results showed that alkalinity reduction is lower in mortars with fly ash compared to those containing cement only. In all the mortars, the porosimetric analysis indicated that porosity is reduced due to carbonation. Further more, it is showed the predominance of the macro and meso...

Construction and Building Materials, 2015

ABSTRACT The main objective of this study is to control restrained plastic shrinkage cracking thr... more ABSTRACT The main objective of this study is to control restrained plastic shrinkage cracking through the addition of natural and PVA fibers in a cement-based composite. Two types of natural fibers (flax and agave lechuguilla) as well as synthetic fibers (PVA) were investigated at volume fractions of 0.1% and 0.7%. 38 prismatic mortar specimens were freshly cast on top of a grooved and hard concrete substrate, providing a bottom restraint; this resulted in cracking in the freshly placed overlay, which was detected as a function of time. The effectiveness of the fibers was evaluated by considering reducing the number of cracks and total crack area under these conditions. The results obtained show that both natural fibers were effective in controlling restrained plastic shrinkage cracking like the commercially available PVA fibers; the total crack areas were also reduced by at least 93% compared with plain mortar specimens.

Cement & Concrete Composites, 2007

This research studied the diagonal tension behavior of 16 beams reinforced with longitudinal bars... more This research studied the diagonal tension behavior of 16 beams reinforced with longitudinal bars and steel fibers. The variable parameters included the concrete compressive strength and the percentage of fibers (0%, 0.5%, 1.0% and 1.5% by volume). The beams were tested under static loads resulting in high diagonal tension stresses. The shear reinforcement was composed of stirrups instrumented with strain

Nanotechnology in Construction 3, 2009

The reported research examined the effect of 5-70 nm SiO 2 nanoparticles on the mechanical proper... more The reported research examined the effect of 5-70 nm SiO 2 nanoparticles on the mechanical properties of nano-cement materials. The strength development of portland cement with nano-SiO 2 and superplasticizing admixture was investigated. Experimental results demonstrate an increase in the compressive and flexural strength of mortars with developed nanoparticles. The distribution of nano-SiO 2 particles within the cement paste plays an essential role and governs the overall performance of these products. Therefore, the addition of a superplasticizer was proposed to facilitate the distribution of nano-SiO 2 particles. Superplasticized mortars with 0.25% of selected nano-SiO 2 demonstrated a 16% increase of 1-day compressive strength, reaching 63.9 MPa; the 28-day strength of these mortars was 95.9 MPa (vs. strength of reference superplasticized mortars of 92.1 MPa). Increase of 28-day flexural strength of superplasticized mortars with selected nano-SiO 2 was 18%, reaching 27.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain composite materials with improved performance.

MRS Proceedings, 2010

The reported research examines the effect of 5-70 nm SiO 2 nanoparticles on the mechanical proper... more The reported research examines the effect of 5-70 nm SiO 2 nanoparticles on the mechanical properties of nanocement materials. The strength development of portland cement with nano-SiO 2 and superplasticizing admixture is investigated. Experimental results demonstrate an increase in the compressive strength of mortars with SiO 2 nanoparticles. The distribution of nano-SiO 2 particles within the cement paste plays an essential role and governs the overall performance of these products. Therefore, the addition of a superplasticizer is proposed to facilitate the distribution of nano-SiO 2 particles. The application of effective superplasticizer and high-speed dispergation are found to be very effective dispersion techniques that improve the strength of superplasticized portland cement mortars, reaching up to 63.9 MPa and 95.9 MPa after aging during 1 and 28 days, respectively. These values compare favorably with the observed compressive strengths of reference portland cement mortars of 53.3 MPa and 86.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain the composite materials with improved performance.

2008 Concrete Bridge Conference, 2008

Abstract: Corrosion of steel reinforcement is the most important durability problem in reinforced... more Abstract: Corrosion of steel reinforcement is the most important durability problem in reinforced concrete structures. Bridges are particularly susceptible to corrosion due to chlorides contained in both sea water and thawing salts, or carbonation because high ...

This research intends to identify both inexpensive and durable construction materials. Steel, gla... more This research intends to identify both inexpensive and durable construction materials. Steel, glass and polymer fibers are feasible, expensive alternatives. Natural fibers can be a real possibility for developing countries, due to the fact that these kinds of fibers are available in great quantities, while they are also renewable. Natural fiber affected mainly by the alkalinity of the cementitiuos matrix in the concrete. The durability of the composite will depend on the protection which the fiber has, and on the impermeability features of the cementitiuos matrix.

Construction and Building Materials, 2019

h i g h l i g h t s New knowledge about the substitution of OPC by fly ash(FA) and limestone fill... more h i g h l i g h t s New knowledge about the substitution of OPC by fly ash(FA) and limestone filler(LF). Appropriate combinations of FA + LF counteracts the setting delays in FA concretes. Appropriate combinations of FA+LF improve resistivity and volume stability.

Journal of Building Physics, 2010

As sustainability moves to the forefront of construction, the utilization of high-volume fly ash ... more As sustainability moves to the forefront of construction, the utilization of high-volume fly ash concrete mixtures to reduce CO2 emissions and cement consumption per unit volume of concrete placed is receiving renewed interest. Concrete mixtures in which the fly ash replaces 50% or more of the Portland cement are both economically and technically viable. This article focuses on a characterization of the thermal properties, namely, specific heat capacity and thermal conductivity, of such mixtures. Both the raw materials and the finished products (mortars and concretes) are evaluated using a transient plane source method. Because the specimens being examined are well hydrated, estimates of the specific heat capacity based on a law of mixtures, with a ‘bound water’ specific heat capacity value being employed for the water in the mixture, provide reasonable predictions of the measured performance. As with most materials, thermal conductivity is found to be a function of density, while a...

Construction and Building Materials, 2012

ABSTRACT

Revista Romana de materiale = Romanian journal of materials = RRM

ABSTRACT

This research covers the characterization of four natural pozzolan materials with igneous origin.... more This research covers the characterization of four natural pozzolan materials with igneous origin. The pozzolanic activity index of natural pozzolan-calcium hydroxide systems was determined using the compressive strength of mortar cubes. The rate of the pozzolanic reaction was determined in pastes with the same mix design that was used to make the mortars, this was achieved measuring the changes in time in the Calcium Hydroxide concentration. This information can be used as a preliminary selection tool, to evaluate the pozzolanic potential of natural pozzolan quarries.

Building and environment, 2007

The main objective of the present research was to provide the housing alternatives to istle zone ... more The main objective of the present research was to provide the housing alternatives to istle zone rural areas in Me´xico, which represent about 10% of the national territory. The proposed solution involved a sustainable portland cement-based composite material, reinforced with high tensile strength natural fibers of ''Agave lecheguilla''.

Canadian Journal of Civil Engineering, 2009

Le comportement mécanique des bétons renforcés de fibres naturelles dépend principalement de l'ad... more Le comportement mécanique des bétons renforcés de fibres naturelles dépend principalement de l'adhérence entre la fibre et la matrice de ciment. Cette adhérence a aussi une certaine influence sur le type d'endommagement de ces matériaux. Cette recherche a été menée sur des fibres naturelles de lecheguilla (Agave lecheguilla). Des essais chimiques, physiques et mécaniques tels que la détermination de la composition chimique, la morphologie, la porosité, l'absorption d'eau et les résistances à la traction et à la flexion ont été réalisés en utilisant ces fibres naturelles. Des observations à l'interface fibre-matrice de ciment ont aussi été effectuées à l'aide du stéréoscope pour évaluer l'effet du milieu alcalin et de différents rapports eau/ciment (E/C) sur la performance de mortier fibré. On a constaté que la résistance mécanique à la traction et à la flexion du matériau composite augmente, d'une part, avec l'augmentation de la longueur et, d'autre part, avec la diminution du volume de fibres utilisé. Le principal type de défaillance observée est l'arrachement des fibres. De plus, l'adhérence entre les fibres et la matrice de ciment est modifiée par les changements volumétriques et l'absorption d'eau relativement élevée. Néanmoins, cette adhérence peut être substantiellement améliorée en faisant un traitement superficiel des fibres à l'aide de solutions chimiques, comme le xylène, et en utilisant des faibles rapports E/C.

Results of interrelated tests for physical-chemical and microstructural properties of four synthe... more Results of interrelated tests for physical-chemical and microstructural properties of four synthetic pozzolanas evaluating the hydration rate in blends with calcium hydroxide are presented. The pozzolanic activity of silica fume, classified fly ash, raw fly ash and commercial metakaolin was estimated. Results showed a clear relationship between the calcium hydroxide consumption and the reactive phase content, specific surface area and porosity of the pozzolans. The calcium hydroxide-silica fume blend consumed 98% of portlandite after 21 days, whereas the system with metakaolin also presented an effective pozzolanic activity with 94% depletion. The fly ashes were the less effective pozzolans of the study.

Nanotechnology has changed our vision, expectations and abilities to control the material world. ... more Nanotechnology has changed our vision, expectations and abilities to control the material world. The developments in nano-science will have a great impact on the field of construction materials. Portland cement, one of the largest commodities consumed by mankind, is obviously the product with great, but not completely explored potential. Better understanding and engineering of complex structure of cement based materials at the nano-level will apparently result in a new generation of concrete, stronger and more durable, with desired stress-strain behavior and possibly possessing the range of newly introduced "smart" properties.

Construction and Building Materials, 2012

h i g h l i g h t s " We studied hemihydrate-slag-pozzolanas pastes with improved performance tha... more h i g h l i g h t s " We studied hemihydrate-slag-pozzolanas pastes with improved performance than plasters. " The main hydration products are gypsum, ettringite and C-S-H. " Density is slightly higher than pure plasters but strength is almost triplicate. " Silica fume additions translate in excellent dimensional stability after 180 days.

The influence of carbonation on mortars containing 25% of fly ash instead of the cementitious mat... more The influence of carbonation on mortars containing 25% of fly ash instead of the cementitious materials was studied. Mortar cylinder specimens were fabricated for 4 different W/C ratios: 0.35, 0.45, 0.55 and 0.65. Mortars with and without fly ash were subjected to an accelerated carbonation process. Volumetric weight, water absorption, compressive strength, water permeability, pH and mercury intrusion porosimetry of the mortar specimens were determined. Due to the fly ash pozzolanic potential, for all W/C ratios, results of the compressive strength tests at 28 days of the mortars with and without fly ash were similar. Mortars with fly ash presented similar water permeability as mortars without fly ash. PH results showed that alkalinity reduction is lower in mortars with fly ash compared to those containing cement only. In all the mortars, the porosimetric analysis indicated that porosity is reduced due to carbonation. Further more, it is showed the predominance of the macro and meso...

Construction and Building Materials, 2015

ABSTRACT The main objective of this study is to control restrained plastic shrinkage cracking thr... more ABSTRACT The main objective of this study is to control restrained plastic shrinkage cracking through the addition of natural and PVA fibers in a cement-based composite. Two types of natural fibers (flax and agave lechuguilla) as well as synthetic fibers (PVA) were investigated at volume fractions of 0.1% and 0.7%. 38 prismatic mortar specimens were freshly cast on top of a grooved and hard concrete substrate, providing a bottom restraint; this resulted in cracking in the freshly placed overlay, which was detected as a function of time. The effectiveness of the fibers was evaluated by considering reducing the number of cracks and total crack area under these conditions. The results obtained show that both natural fibers were effective in controlling restrained plastic shrinkage cracking like the commercially available PVA fibers; the total crack areas were also reduced by at least 93% compared with plain mortar specimens.

Cement & Concrete Composites, 2007

This research studied the diagonal tension behavior of 16 beams reinforced with longitudinal bars... more This research studied the diagonal tension behavior of 16 beams reinforced with longitudinal bars and steel fibers. The variable parameters included the concrete compressive strength and the percentage of fibers (0%, 0.5%, 1.0% and 1.5% by volume). The beams were tested under static loads resulting in high diagonal tension stresses. The shear reinforcement was composed of stirrups instrumented with strain

Nanotechnology in Construction 3, 2009

The reported research examined the effect of 5-70 nm SiO 2 nanoparticles on the mechanical proper... more The reported research examined the effect of 5-70 nm SiO 2 nanoparticles on the mechanical properties of nano-cement materials. The strength development of portland cement with nano-SiO 2 and superplasticizing admixture was investigated. Experimental results demonstrate an increase in the compressive and flexural strength of mortars with developed nanoparticles. The distribution of nano-SiO 2 particles within the cement paste plays an essential role and governs the overall performance of these products. Therefore, the addition of a superplasticizer was proposed to facilitate the distribution of nano-SiO 2 particles. Superplasticized mortars with 0.25% of selected nano-SiO 2 demonstrated a 16% increase of 1-day compressive strength, reaching 63.9 MPa; the 28-day strength of these mortars was 95.9 MPa (vs. strength of reference superplasticized mortars of 92.1 MPa). Increase of 28-day flexural strength of superplasticized mortars with selected nano-SiO 2 was 18%, reaching 27.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain composite materials with improved performance.

MRS Proceedings, 2010

The reported research examines the effect of 5-70 nm SiO 2 nanoparticles on the mechanical proper... more The reported research examines the effect of 5-70 nm SiO 2 nanoparticles on the mechanical properties of nanocement materials. The strength development of portland cement with nano-SiO 2 and superplasticizing admixture is investigated. Experimental results demonstrate an increase in the compressive strength of mortars with SiO 2 nanoparticles. The distribution of nano-SiO 2 particles within the cement paste plays an essential role and governs the overall performance of these products. Therefore, the addition of a superplasticizer is proposed to facilitate the distribution of nano-SiO 2 particles. The application of effective superplasticizer and high-speed dispergation are found to be very effective dispersion techniques that improve the strength of superplasticized portland cement mortars, reaching up to 63.9 MPa and 95.9 MPa after aging during 1 and 28 days, respectively. These values compare favorably with the observed compressive strengths of reference portland cement mortars of 53.3 MPa and 86.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain the composite materials with improved performance.