Industrialised Mass Housing in Saudi Arabia: A Qualitative and Technological Study

In 2017, the Saudi Arabian Government through its Ministry of Housing, announced that it planned to build 1.45 million affordable houses by 2030. The government will contribute to the cost of the houses to put them within the price range of people with modest incomes. Central to achieving this goal is the use of innovative, high-tech construction methods, mainly 3D printing. Several prototype houses have been constructed and more are planned to give Saudis an opportunity to experience them first-hand before a decision is made to go ahead with the planned rollout. The motivation for this thesis was to better understand the likely success or failure of this ambitious scheme. Early research soon revealed that since the discovery of oil in the kingdom in 1938, there have been many thousands of houses and apartments built through government-sponsored affordable housing projects. All have embodied a mixture of imported western notions of domestic living combined with traditional Saudi cultural, social and religious values and practices. The construction of these large-scale projects has relied on, and to a large extent been driven by, the use of imported construction materials, techniques and expertise. To better understand the current masshousing plan this thesis, through the study of examples and case studies, explores these projects from both a technological and a qualitative perspective. The aim is to provide insights into their successes and failures in the hope that lessons can be learned that will help guide the current proposal towards a fruitful outcome for the Saudi people for whom the houses are intended. Prior to 1938, domestic buildings in Saudi Arabia were constructed by local craftsmen using traditional materials and techniques. The first modern buildings were, flat-packed, timber houses manufactured in California and imported by the Standard Oil Company of California (SOCAL) to accommodate their expat oil workers in the rapidly expanding camp at Dammam on the Arabian Gulf. A trickle soon turned into a flood with many thousands of prefabricated timber houses from America and Europe imported into oil compounds all around the country. While these houses were never accepted more widely by Saudis as suitable domestic dwellings the modernist, technological thinking they embodied undoubtedly translated into the first contemporary, non-traditional houses built outside the camps during the 1950s designed by architects and engineers employed by SOCAL’s successor company Aramco. Mass-housing projects for the wider Saudi community soon followed all of which were constructed with heavy concrete construction. The first examples were built in situ however by the 1970s industrialised prefabrication had become established as the dominant method of delivering thousands of identical, affordable houses and apartments. Many were initially unappealing to Saudi house and apartment buyers and stood empty for a number of years. When the houses were finally occupied their new owners expressed their dissatisfaction with the manifestation of imported ideas about how they should live by almost universally carrying out modifications. These range from the relatively minor, raising the height of boundary walls, to major changes including adding a second storey. It is extremely difficult for the untrained householder or the local builder to alter and modify a house constructed of factory-made, loadbearing precast concrete panels and the same will be true for 3D printed houses. For the 1970s precast houses, modifications resulted in a significant number of structural failures leading to abandonment of the house. In addition, eclectic streetscapes emerged consisting of an assortment of styles and building materials some of which attempt to recreate a resonance with vernacular modes of living. Some houses are modelled on the latest trends found in architectural and lifestyle magazines. If minimising this level of modification is accepted as a goal for the proposed 3D printed houses, then a detailed understanding of previous industrialised mass housing schemes is important.Thesis (Ph.D.) -- University of Adelaide, School of Architecture & Built Environment, 202

Properties of model E-glass fiber composites with varying matrix monomer ratios

ObjectiveTo evaluate properties of fiber-reinforced-composites (FRC) containing Bis-EMA/UDMA monomers but identical dispersed phase (60% wt BaSi glass power +10% wt E-glass fibre).MethodsA control (Group A), monomer mixture comprising 60% Bis-GMA, 30% TEGDMA, and 10% PMMA (typical FRC monomers) was used. The following monomer mass fractions were mixed: 50% bis-GMA plus 50% of different ratios of Bis-EMA+UDMA to produce consistent formulations (Groups B-E) of workable viscosities was also studied. Flexural strength (FS), fracture toughness (KIC), water sorption (SP), solubility (SL) and hygroscopic expansion (HE) were measured. FS and KIC specimens were stored for 1, 7 d, and 30 d in water at 37 °C. SP/SL specimens were water-immersed for 168d, weighed at intervals, then dried for 84 d at 37 °C. To analyze differences in FS, and KIC, a two-way ANOVA and Tukey post-hoc tests (α = 0.05) were conducted. For SP/SL, and HE, one-way ANOVA with subsequent Tukey post-hoc tests (α = 0.05) were utilized.ResultsFS and KIC for groups A, D, E decreased progressively after 1 d. Groups B and C (highest amounts of Bis-EMA) did not decrease significantly. The modified matrix composites performed significantly better than the control group for SP and HE. The control group outperformed the experimental composites only for SL with up to 250% higher SL for group E (6.9 μg/mm) but still below the maximum permissible threshold of 7.5 μg/mm. Significance:Experimentalcomposites with highest amounts of Bis-EMA showed improved hydrolytic stability and overall enhancement in several clinically-relevant properties. This makes them potential candidates for alternative matrices to a semi-interpenetrating network in fiber-reinforced composites

Synthesis and characterisation of microcapsules for self-healing dental resin composites

Aim: The purpose of this study was to i) synthesise TEGDMA-DHEPT microcapsules in a laboratory setting; ii) characterise the resultant microcapsules for quality measures. Materials &amp; methods: Microcapsules were prepared by in situ polymerization of PUF shells. Microcapsules characterisation include size analysis, optical and SEM microscopy to measure the diameter and analyse the morphology of PUF microcapsules. FT-IR spectrometer evaluated microcapsules and benzyl peroxide catalyst polymerization independently. Result: Average diameter of TEGDMA-DHEPT microcapsules was 120 ± 45 μm (n: 100). SEM imaging of the capsular shell revealed a smooth outer surface with deposits of PUF nanoparticles that facilitate resin matrix retention to the microcapsules upon composite fracture. FT-IR spectra showed that microcapsules crushed with BPO catalyst had degree of conversion reached to 60.3%. Conclusion: TEGDMA-DHEPT microcapsules were synthesised according to the selected parameters. The synthesised microcapsules have a self-healing potential when embedded into dental resin composite as will be demonstrated in our future work. Graphical Abstract: Graphical abstract showing the microcapsule components. The shell contains poly(urea-formaldehyde), and the core consists of TEGDMA-DHEPT healing agents.[Figure not available: see fulltext.].</p

Properties of A Model Self-Healing Microcapsule-Based Dental Composite Reinforced with Silica Nanoparticles

Aim: The purpose of this study was to evaluate the mechanical properties of an experimental self-healing dental composite model (SHDC) composed of SiO(2) nanoparticles with varying percentages of triethylene glycol dimethacrylate (TEGDMA) monomer and N,N-dihydroxyethyl-p-toluidine (DHEPT) amine microcapsules. Materials and methods: Microcapsules were prepared by in-situ polymerisation of PUF shells, as explained in our previous work. The model SHDC included bisphenol A glycidyl dimethacrylate (Bis-GMA:TEGDMA) (1:1), 1 wt% phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide (BAPO), 0.5 wt% benzoyl peroxide (BPO) catalyst, 20 wt% silanised silica dioxide (SiO(2)) (15 nm) and (0, 2.5, 5, 7.5, 10 wt%) of microcapsules (120 ± 45 μm). Light transmission, hardness, degree of conversion (DC), flexural strength and elastic modulus of the SHDC model were measured. Results: The degree of conversion of the SHDC ranged from 73 to 76% 24 h after polymerisation. Hardness measurements ranged from 22 to 26 VHN (p > 0.05); however, the flexural strength was adversely affected from 80 to 55 MPa with increasing microcapsules of up to 10 wt% in the composites (p 10 wt%) in the composites. All other measured properties were not significantly affected. Accordingly, we recommend a stronger composite material that could be created by increasing the filler content distribution in order to achieve a hybrid self-healing composite with enhanced mechanical properties

Temperature rise in photopolymerized adhesively-bonded resin composite: A thermography study

ObjectivesTo assess visually and quantitatively the contributions of the adhesive layer photopolymerization and the subsequent resin composite increment to spatio-temporal maps of temperature at five different cavity locations, subjected to two irradiance curing protocols: standard and ultra-high.MethodsCaries-free molars were used to obtain 40, 2 mm thick dentin slices, randomly assigned to groups (n = 5). These slices were incorporated within 3D-printed model cavites, 4 mm deep, restored with Adhese® Universal bonding agent and 2 mm thick Tetric® Powerfill resin composite, and photocured sequentially, as follows: G1: control-empty cavity; G2: adhesive layer; G3 composite layer with no adhesive; and G4 composite layer with adhesive. The main four groups were subdivided based on two curing protocols, exposed either to standard 10 s (1.2 W/cm2) or Ultra high 3 s (3 W/cm2) irradiance modes using a Bluephase PowerCure LCU. Temperature maps were obtained, via a thermal imaging camera, and numerically analyzed at 5 locations. The data were analyzed using two-way ANOVA followed by multiple one-way ANOVA, independent t-tests and Tukey post-hoc tests (α = 0.05). Tmax, ΔT, Tint (integrated area under the curve) and time-to-reach-maximum-temperature were evaluated.ResultsTwo-way ANOVA showed that there was no significant interaction between light-curing time and location on the measured parameters (p &gt; 0.05), except for the time-to-reach-maximum-temperature (p &lt; 0.05). Curing the adhesive layer alone with the 10 s protocol resulted in a significantly increased pulpal roof temperature compared to 3 s cure (p &lt; 0.05). Independent T-tests between G3 and G4, between 3 s and 10 s, confirmed that the adhesive agent caused no significant increases (p &gt; 0.05) on the measured parameters. The ultra-high light-curing protocol significantly increased ΔT in composite compared to 10 s curing (p &lt; 0.05).SignificanceWhen the adhesive layer was photocured alone in a cavity, with a 2 mm thick dentin floor, the exothermal release of energy resulted in higher temperatures with a 10 s curing protocol, compared to a 3 s high irradiance. But when subsequently photocuring a 2 mm layer of composite, the resultant temperatures generated at pulpal roof location from the two curing protocols were similar and therefore there was no increased hazard to the dental pulp from the immediately prior adhesive photopolymerization, cured via the ultra-high irradiation protocol

Ceramic and Composite Polishing Systems for Milled Lithium Disilicate Restorative Materials: A 2D and 3D Comparative In Vitro Study.

Purpose: This study aims to evaluate the effectiveness of two ceramic and two composite polishing systems for a novel chairside computer-aided design/computer-aided manufacturing (CAD/CAM) lithium disilicate ceramic with three-dimensional and two-dimensional microscopy images. This ceramic material can be used for implant-supported or tooth-borne single-unit prostheses. Materials and Methods: Sixty flat samples of novel chairside CAD/CAM reinforced lithium disilicate ceramic (Amber Mill, Hass Bio) were divided into five groups (n = 15/group) and treated as follows: Group 1 (NoP), no polished treatment; group 2 (CeDi), polished with ceramic Dialite LD (Brasseler USA); group 3, (CeOp) polished with ceramic OptraFine (Ivoclar Vivadent); group 4, (CoDi) polished with composite DiaComp (Brasseler USA), and group 5 (CoAs), polished with composite Astropol (Ivoclar Vivadent). The polished ceramic surface topography was observed and measured with three-dimensional and two-dimensional images. Results: All polishing systems significantly reduced the surface roughness compared with the non-polished control group (Sa 1.15 μm). Group 2 (CeDi) provided the smoothest surface arithmetical mean eight with 0.32 μm, followed by group 3 (CeOp) with 0.34 μm. Group 5 (CoAs) with 0.52 μm provided the smoothest surface among the composite polishing kits. Group 4 (CoDi) with 0.66 μm provided the least smooth surface among all polishing systems tested. Conclusions: Despite the effectiveness of ceramic polishing systems being superior to composite polishing systems of the CAD/CAM lithium disilicate restorative material, both polishing systems significantly improved the smoothness

Biomimetic Whitening Effect of Polyphosphate-Bleaching Agents on Dental Enamel.

This in vitro study investigated the extrinsic tooth-whitening effect of bleaching products containing polyphosphates on the dental enamel surface compared to 10% carbamide peroxide (CP). Eighty human molars were randomly allocated into four whitening-products groups. Group A (control) was treated with 10% CP (Opalescence). The other groups with non-CP over-the-counter (OTC) products were group B = polyphosphates (iWhiteWhitening-Kit); group C = polyphosphates+fluoride (iWhite-toothpaste); and group D = sodium bicarbonate (24K-Whitening-Pen). L*, a*, b* color-parameters were spectrophotometer-recorded at baseline (T0), one day (T1), and one month (T2) post-treatment. Changes in teeth color (ΔEab) were calculated. Data were analyzed using ANOVA and the Bonferroni test (α = 0.05). Groups A, B, and D showed significant differences in ΔL*&Δa* parameters at T1, but not in Δb* at T0. Group C showed no difference for ΔL*, Δa*, Δb* at T0 and T1. Group A showed differences for ΔL*, Δa*, Δb*, at T2, while groups B, C, and D had no difference in any parameters at T0. At T1, ΔEab values = A &gt; D&gt; B &gt; C (ΔEab = 13.4 &gt; 2.4 &gt; 2.1 &gt; 1.2). At T2, ΔEab values increased = A &gt; B &gt; C &gt; D (ΔEab = 12.2 &gt; 10.6 &gt; 9.2 &gt; 2.4). In conclusion, the 10% CP and Biomimetic polyphosphate extrinsic whitening kit demonstrated the highest color change, while simulated brushing with dark stain toothpaste and a whitening pen demonstrated the lowest color change at both measurement intervals