Pedro Valdez - Academia.edu (original) (raw)

Papers by Pedro Valdez

Cement & Concrete Composites

This article presents experimental research work oriented toward developing practical design tool... more This article presents experimental research work oriented toward developing practical design tools for industrial application, and illustrates the potential benefits of the synergistic effect of an ASTM C 618 Class F fly ash (FA) and a high-range polycarboxylate superplasticizer (SP) in the production of conventional concrete. The different concretes considered in this study were produced with mass substitutions of cement by FA between 15% and 75%, and a target slump of 200 mm ± 20 mm. The total water content was minimized through the use of an optimum SP dosage that resulted in water reductions of 18%, 15% and 11% respectively for the reference mixtures of w/b = 0.5, w/b = 0.55, and w/b = 0.6, which leads to the same percentage reductions of cement. Heat release and heat flow were analyzed through isothermal and semi-adiabatic calorimetry, illustrating that heat release per unit mass of cement is independent of w/b, contrasting with the time of setting results that vary by several hours between the three different w/b ratios. The paper highlights the beneficial effect of the SP in terms of cement reduction and slump retention. Correlations between the FA substitution and slump loss, setting times, compressive strength and static modulus of elasticity (E) were established and they represent very useful tools for the practical applications of the results. Compressive strength developments up to an age of 56 d are also reported, as well as correlations between the modulus of rupture and compressive strength or splitting tensile strength at an age of 28 d.

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.

The reported research examined the effect of 5-70 nm SiO2 nanoparticles on the mechanical propert... more The reported research examined the effect of 5-70 nm SiO2 nanoparticles on the mechanical properties of nano-cement materials. The strength development of portland cement with nano-SiO2 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-SiO2 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-SiO2 particles. Superplasticized mortars with 0.25% of selected nano-SiO2 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-SiO2 was 18%, reaching 27.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain composite materials with improved performance.

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 gages to detect the effect of the fibers on the strains. Research results indicate that as the fiber volume increases, the shear strength and the ductility of the beams increased, providing significantly higher shear strength than specified by the ACI-318 Code.

Transportation Research Record, 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.

Cement & Concrete Composites

This article presents experimental research work oriented toward developing practical design tool... more This article presents experimental research work oriented toward developing practical design tools for industrial application, and illustrates the potential benefits of the synergistic effect of an ASTM C 618 Class F fly ash (FA) and a high-range polycarboxylate superplasticizer (SP) in the production of conventional concrete. The different concretes considered in this study were produced with mass substitutions of cement by FA between 15% and 75%, and a target slump of 200 mm ± 20 mm. The total water content was minimized through the use of an optimum SP dosage that resulted in water reductions of 18%, 15% and 11% respectively for the reference mixtures of w/b = 0.5, w/b = 0.55, and w/b = 0.6, which leads to the same percentage reductions of cement. Heat release and heat flow were analyzed through isothermal and semi-adiabatic calorimetry, illustrating that heat release per unit mass of cement is independent of w/b, contrasting with the time of setting results that vary by several hours between the three different w/b ratios. The paper highlights the beneficial effect of the SP in terms of cement reduction and slump retention. Correlations between the FA substitution and slump loss, setting times, compressive strength and static modulus of elasticity (E) were established and they represent very useful tools for the practical applications of the results. Compressive strength developments up to an age of 56 d are also reported, as well as correlations between the modulus of rupture and compressive strength or splitting tensile strength at an age of 28 d.

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.

The reported research examined the effect of 5-70 nm SiO2 nanoparticles on the mechanical propert... more The reported research examined the effect of 5-70 nm SiO2 nanoparticles on the mechanical properties of nano-cement materials. The strength development of portland cement with nano-SiO2 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-SiO2 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-SiO2 particles. Superplasticized mortars with 0.25% of selected nano-SiO2 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-SiO2 was 18%, reaching 27.1 MPa. It is concluded that the effective dispersion of nanoparticles is essential to obtain composite materials with improved performance.

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 gages to detect the effect of the fibers on the strains. Research results indicate that as the fiber volume increases, the shear strength and the ductility of the beams increased, providing significantly higher shear strength than specified by the ACI-318 Code.

Transportation Research Record, 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.