Performance of Periwinkle Shell Ash Blended Cement Concrete Exposed to Magnesium Sulphate

The study examined the compressive strength of periwinkle shell ash (PSA) blended cement concrete in magnesium sulphate medium. Specimens were prepared from designed characteristics strength of 25 MPa. The cement replacement with PSA ranged between 0 and 40% by volume. A total of 180 cube specimens were cast and cured in water. At 28 days curing, 45 specimens each were transferred into magnesium sulphate of 1%, 3%, and 5% solution, while others were continuously cured in water and tested at 62, 92, and 152 days. The results revealed a higher loss in compressive strength with the control mix, and that it increases with increased in MgSO4 concentration and exposure period, whereas, the attack on the PSA blended cement concrete was less and the least value recorded by 10% PSA content. Therefore, the study concluded that the optimum percentage replacement of cement with 10% PSA could mitigate magnesium sulphate attack

MAT-742: EFFECT OF SUPPLEMENTARY CEMENTITIOUS MATERIALS ON THE RESISTANCE OF MORTAR TO PHYSICAL SULFATE SALT ATTACK

Physical sulfate salt attack is one of the most rapid and severe deterioration mechanisms in concrete structures. One of the most common approaches to improve resistance of concrete to sulfate attack is to use supplementary cementitious materials. However, physical salt attack may still cause damage to concrete with supplementary cementitious materials. Moreover, according to some literature sources, some supplementary cementitious materials may even reduce resistance to physical salt attack. The current research investigates the effect of supplementary cementitious materials on the ability of mortars to resist physical sulfate salt attack and its relationship with pore structure and transport properties. Mortar specimens with 45 and 65% replacement of cement by ground-granulated blast-furnace slag and with 20 and 40% replacement of cement by fly ash were exposed to physical sulfate attack. The results show a good correlation between the pore microstructure and transport properties to the resistance to physical salt attack. Ground-granulated blast-furnace slag was found to improve the resistance to physical salt attack, while fly ash demonstrated a negative effect

An Accuracy-Assured Privacy-Preserving Recommender System for Internet Commerce

Recommender systems, tool for predicting users' potential preferences by computing history data and users' interests, show an increasing importance in various Internet applications such as online shopping. As a well-known recommendation method, neighbourhood-based collaborative filtering has attracted considerable attention recently. The risk of revealing users' private information during the process of filtering has attracted noticeable research interests. Among the current solutions, the probabilistic techniques have shown a powerful privacy preserving effect. When facing $k$ Nearest Neighbour attack, all the existing methods provide no data utility guarantee, for the introduction of global randomness. In this paper, to overcome the problem of recommendation accuracy loss, we propose a novel approach, Partitioned Probabilistic Neighbour Selection, to ensure a required prediction accuracy while maintaining high security against $k$NN attack. We define the sum of $k$ neighbours' similarity as the accuracy metric alpha, the number of user partitions, across which we select the $k$ neighbours, as the security metric beta. We generalise the $k$ Nearest Neighbour attack to beta k Nearest Neighbours attack. Differing from the existing approach that selects neighbours across the entire candidate list randomly, our method selects neighbours from each exclusive partition of size $k$ with a decreasing probability. Theoretical and experimental analysis show that to provide an accuracy-assured recommendation, our Partitioned Probabilistic Neighbour Selection method yields a better trade-off between the recommendation accuracy and system security.Comment: replacement for the previous versio

Poseidon: Mitigating Interest Flooding DDoS Attacks in Named Data Networking

Content-Centric Networking (CCN) is an emerging networking paradigm being considered as a possible replacement for the current IP-based host-centric Internet infrastructure. In CCN, named content becomes a first-class entity. CCN focuses on content distribution, which dominates current Internet traffic and is arguably not well served by IP. Named-Data Networking (NDN) is an example of CCN. NDN is also an active research project under the NSF Future Internet Architectures (FIA) program. FIA emphasizes security and privacy from the outset and by design. To be a viable Internet architecture, NDN must be resilient against current and emerging threats. This paper focuses on distributed denial-of-service (DDoS) attacks; in particular we address interest flooding, an attack that exploits key architectural features of NDN. We show that an adversary with limited resources can implement such attack, having a significant impact on network performance. We then introduce Poseidon: a framework for detecting and mitigating interest flooding attacks. Finally, we report on results of extensive simulations assessing proposed countermeasure.Comment: The IEEE Conference on Local Computer Networks (LCN 2013

Effect of Microsilica and Water Proofer on Resistance of Concrete to Phosphoric Acid Attack

This paper investigates the effect of microsilica (MS), water proofer (WP) and MS-WP contents on the durability of concrete to phosphoric acid attack. Three MS replacement levels and three WP mixes were considered in the study: 10%, 15% and 20% by weight of cement for MS and mixes of 0.4, 0.6 and 0.8 L for WP. The water to cement ratio was considered to be constant. The workability, durability of concrete to freezing thawing after 300 cycles, durability of concrete to phosphoric acid attack after 15 cycles of wetting and drying in phosphoric acid solution, compressive strength and modulus of rupture after 28 days were investigated. The degree of acid attack was evaluated by measuring the loss in weight. The study showed that the combined effect of MS-WP improved the durability of concrete to freezing thawing and to phosphoric acid attack without significantly reducing the compressive strength or modulus of rupture of the concrete. The optimum mix was 10% of MS replacement and 0.8 L of WP

The effect of atomic oxygen on polysiloxane-polyimide for spacecraft applications in low Earth orbit

Polysiloxane-polyimide films are of interest as a replacement for polyimide Kapton in the Space Station Freedom solar array blanket. The blanket provides the structural support for the solar cells as well as providing transport of heat away from the back of the cells. Polyimide Kapton would be an ideal material to use; however, its high rate of degradation due to attack by atomic oxygen in low Earth orbit, at the altitudes Space Station Freedom will fly, is of such magnitude that if left unprotected, the blanket will undergo structural failure in much less than the desired 15 year operating life. Polysiloxane-polyimide is of interest as a replacement material because it should from its own protective silicon dioxide coating upon exposure to atomic oxygen. Mass, optical, and photomicrographic data obtained in the evaluation of the durability of polysiloxane-polyimide to an atomic oxygen environment are presented

Influence of Reclaimed Asphalt Pavement Aggregates on Strength and Durability Properties of Concrete Mixes in Rigid Pavements

The use of Reclaimed Asphalt Pavement (RAP) aggregates in rigid pavements instead of conventional aggregates in Himalayan regions solves the problem associated with shrinking natural resources and dumping of wastes. This study studied the effect of partial replacement of conventional coarse aggregates by RAP in Dry Lean Concrete (DLC) mixes suitable for rigid pavements. A total of 114 specimens (cubical and cylindrical) were cast and tested for mechanical and durability properties as per ASTM and IS code guidelines, partially replaced with CRAP by 25%, 50%, and 75% by weight. The simultaneous effect of fly ash addition by partial replacement of cement by it was also studied. The study concludes that 25% partial replacement by CRAP with 10% fly ash as partial replacement of cement led to the achievement of the strength benchmark as mandated by IRC SP 44 (2014). It was also observed that durability properties such as resistance to acid attack, sulphate attack and carbonation also improved in DLC mixes, including CRAP and fly ash, when compared to control mixes. 

Formal verification of a software countermeasure against instruction skip attacks

Fault attacks against embedded circuits enabled to define many new attack paths against secure circuits. Every attack path relies on a specific fault model which defines the type of faults that the attacker can perform. On embedded processors, a fault model consisting in an assembly instruction skip can be very useful for an attacker and has been obtained by using several fault injection means. To avoid this threat, some countermeasure schemes which rely on temporal redundancy have been proposed. Nevertheless, double fault injection in a long enough time interval is practical and can bypass those countermeasure schemes. Some fine-grained countermeasure schemes have also been proposed for specific instructions. However, to the best of our knowledge, no approach that enables to secure a generic assembly program in order to make it fault-tolerant to instruction skip attacks has been formally proven yet. In this paper, we provide a fault-tolerant replacement sequence for almost all the instructions of the Thumb-2 instruction set and provide a formal verification for this fault tolerance. This simple transformation enables to add a reasonably good security level to an embedded program and makes practical fault injection attacks much harder to achieve

Chemical Attack of Malaysian Pozzolans Concrete

Malaysia produces more than 10 million tonne of by-product from industrial sector per year. As the environmental impact concerns, more than half of the by-product can be recycled to be used as construction materials. One of them is pozzolan, a cement replacing material that can be used to enhance the properties of the concrete. This paper studies the chemical attack to local prozzolans concrete. The parameters studied include weight loss, length change, and residual strength of local pozzolans concrete after been exposed to severe environment. The specimen were tested under normal room temperature, exposed to magnesium sulfate, MgSO4. 2H2O where both sulfate attack and acid attack take place. Two series of pozzolans< which is Pulverized fly ash (PFA) and Palm oil fuel ash (POFA) were identified. Another series of admixture, Quarry Dust (QD) from quarry waste that contain high amount of silica content also been carried out. Each series will study the effect of cement replacement percentage of 5%, 10% and 15%. The parameters were compared to conventional ordinary Portland cement (OPC) concrete as control mix. Accelerated testing was conducted at 3, 7, 28, 56 and 90 days. The result shows that the local pozzolans concrete were found to be in good resistance against sulfate attack compared to conventional concrete. Compared to all series conducted, series of PFA replacement gave the best resistance followed by POFA and QD replacement series